Management of incidentally detected heart murmurs in dogs and cats

Abstract

A dog or a cat has an incidentally detected heart murmur if the murmur is an unexpected discovery during a veterinary consultation that was not initially focused on the cardiovascular system. This document presents approaches for managing dogs and cats that have incidentally-detected heart murmurs, with an emphasis on murmur characteristics, signalment profiling, and multifactorial decision-making to choose an optimal course for a given patient.

Full text

1076 Vet Med Today: Reference Point JAVMA, Vol 246, No. 10, May 15, 2015
A
dog or a cat has an incidentally detected heart
murmur if the murmur is an unexpected discov-
ery during a veterinary consultation that was not ini-
tially focused on the cardiovascular system. Common
examples include auscultation of a murmur during an
annual wellness examination, prior to general anesthe-
sia, or during evaluation of a patient for a noncardiac
medical condition.
Successful management of an animal with an inci-
dentally detected heart murmur requires a correct diag-
nosis to accomplish the goals of accurate prognostica-
tion, appropriate initiation of treatment if needed, and
having a satisfied client who fully understands the im-
plications of the murmur, including the impact of the
underlying disorder on the animal’s health. This docu-
ment provides current information by species and age
group to help veterinarians make appropriate decisions
and initial diagnostic plans after incidental detection of
a murmur in a dog or cat.
An incidentally detected heart murmur might or
might not require further diagnostic investigation. De-
finitive diagnosis of the cause of a murmur benefits the
patient because it serves as the basis for providing an
appropriate level of treatment and monitoring. It also
provides value for the client (by allowing an accurate
assessment of presence and severity of disease in the
pet and its prognosis) and for the veterinarian (by cor-
roborating or expanding on auscultatory findings and
on understanding of the impact that a given condition
can have on the patient). In general, the veterinarian
who has detected a murmur is in the best position to
develop the initial diagnostic and case management
Management of incidentally detected
heart murmurs in dogs and cats
plans in conjunction with the client, given the veteri-
narian’s familiarity with the patient, the client, and the
characteristics of the murmur as determined by careful
auscultation.
The first and often most challenging step is to de-
termine the clinical importance of a murmur. Its char-
acteristics may suggest that it most likely results from
a cardiovascular lesion (termed pathological murmur)
or that it most likely is associated with a structurally
normal heart (termed nonpathological murmur). The
terms nonpathological murmur, functional murmur,
innocent murmur, and flow murmur are similar inas-
much as they all signify that a murmur is not caused
by a structural cardiovascular lesion; however, each has
a specific meaning (Figure 1).
1
In this document, non-
pathological murmur will be used as the principal term
to describe murmurs that are not associated with struc-
tural cardiovascular lesions.
Veterinarians investigating the clinical importance
of a heart murmur should optimally include the follow-
ing steps in the patient’s evaluation:
• Determine, by careful auscultation, whether the
murmur is most likely to be pathological or non-
pathological (Appendices 1 and 2).
1–3
A veterinar-
ian’s ability to make this determination increases
with experience in auscultation of dogs,
4
but often
it is not possible to classify systolic murmurs of in-
tensity grades 1/6 through 3/6 as clearly pathologi-
cal or nonpathological in cats.
• When auscultation reveals that the murmur is con-
vincingly nonpathological, identify and address the
systemic disorder likely causing the murmur (eg,
anemia), if any. In the absence of a systemic cause,
the purpose of further cardiovascular diagnostic
tests is confirmation that the heart is structurally
normal.
Reference Point
ABBREVIATIONS
CHF Congestive heart failure
CKCS Cavalier King Charles Spaniel
DCM Dilated cardiomyopathy
DMVD Degenerative or myxomatous
atrioventricular valve disease
NT-proBNP Amino-terminal pro-B-type natriuretic
peptide
VHS Vertebral heart score
VSD Ventricular septal defect
From the Department of Companion Animals, Atlantic Veterinary College,
University of Prince Edward Island, Charlottetown, PE C1A 4P3, Canada
(Côté); Upstate Veterinary Specialties, 222 Troy Schenectady Rd, Latham,
NY 12110 (Edwards); VetCorp Inc, PO Box 1946, Mammoth Lakes, CA
93546 (Ettinger); the Department of Clinical Sciences and Services, Royal
Veterinary College, University of London, Hatfield, Hertfordshire, AL9
7TA, England (Luis Fuentes); VCA Animal Care Center of Sonoma Coun-
ty, 6470 Redwood Dr, Rohnert Park, CA 94928 (MacDonald); the Depart-
ment of Veterinary Clinical Sciences, College of Veterinary Medicine, The
Ohio State University, Columbus, OH 43210 (Scansen); the Department
of Small Animal Services, College of Veterinary Medicine, Oregon State
University, Corvallis, OR 97331 (Sisson); and the Department of Small
Animal Clinical Sciences, Virginia-Maryland Regional College of Veteri-
nary Medicine, Virginia Polytechnic Institute and State University, Blacks-
burg, VA 24061 (Abbott).
Prepared by the Working Group of the American College of Veterinary Internal
Medicine Specialty of Cardiology on Incidentally Detected Heart Murmurs.
Address correspondence to Dr. Côté (ecote@upei.ca).
Etienne Côté, DVM; N. Joel Edwards, DVM; Stephen J. Ettinger, DVM; Virginia Luis Fuentes, VetMB, PhD;
Kristin A. MacDonald,
DVM, PhD; Brian A. Scansen, DVM, MS; D. David Sisson, DVM; Jonathan A. Abbott, DVM

JAVMA, Vol 246, No. 10, May 15, 2015 Vet Med Today: Reference Point 1077
• When auscultation reveals that the murmur is patho-
logical, or could be either pathological or nonpatho-
logical, use additional information to prioritize dif-
ferential diagnoses according to likelihood and refine
the initial case management plan. This should in-
clude assessment of all of the murmur’s auscultatory
features (eg, where it is heard the loudest [point of
maximal intensity: right or left side of the thorax,
over the base or apex of the heart], whether it radiates
and if so, to which regions of the thorax [or beyond],
the frequency characteristics and sound quality of the
murmur, and whether it is limited to systole). Con-
currently, findings from the remainder of the physical
examination, particularly mucous membrane color,
femoral pulse quality, heart rate and rhythm, and re-
spiratory rate should be considered carefully. Finally,
the patient’s age, breed, sex, and body size can help
the veterinarian consider certain disorders to be more
plausible, or less so, in a specific patient (signalment
profiling). Together, these elements should be used
for creating a differential diagnosis list ranging from
most likely to least likely conditions.
Several important factors then help the veterinar-
ian and client determine whether cardiovascular diag-
nostic testing will be pursued. Indications for further
testing include suspicion of a pathological murmur on
the basis of auscultatory features or difficulty in in-
terpreting the murmur; presence of additional abnor-
mal heart sounds; detection of overt clinical signs that
could be referable to cardiac disease; need to investigate
whether a new murmur is associated with other, seem-
ingly unrelated, findings (eg, shifting leg lameness that
could be associated with infective endocarditis); client
concern, anxiety, or desire to be fully aware of the cause
of the murmur and associated prognosis and treatment
options; the animal’s intended use; whether an event
or intervention that could increase the risk of arrhyth-
mia, CHF, or thromboembolism (eg, general anesthesia
or plane travel) is imminent; and the availability, cost,
and perceived value of diagnostic tests (Figure 2). Two
patients could have identical heart murmurs but be
evaluated differently on the basis of differences in these
factors. Ultimately, the murmur must be evaluated to a
degree that is appropriate for the patient and acceptable
to the veterinarian and the client (Figure 3).
Heart Murmurs in Puppies
Dogs can be considered pediatric patients when
they are between 6 weeks of age and the age of full adult
height and normal organ physiology (6 months in toy
breeds; ≥ 1 year in giant breeds).
5
Nonpathological mur-
murs are commonly recognized in puppies, although
objective information on prevalence and temporal evo-
lution is scarce.
6
The characteristics of nonpathological
murmurs are described (Appendix 1); anecdotally, the
often-noted musical qualities of nonpathological mur-
Figure 1—Nomenclature of pathological and nonpathological heart murmurs.
1

1078 Vet Med Today: Reference Point JAVMA, Vol 246, No. 10, May 15, 2015
murs detected in human patients are less commonly
identified in dogs. Nonpathological murmurs also can
be caused by such systemic disturbances as anemia,
and evaluation for noncardiac disorders is warranted in
puppies with incidentally detected murmurs and a his-
tory or physical examination findings consistent with
noncardiac disease.
Pathological murmurs in puppies typically result
from congenital heart malformations. The overall prev-
alence of congenital heart disease has been estimated to
be 4.6 to 8.5 per thousand in clinical populations.
7
The
most common congenital heart defects reported in dogs
in the United States include pulmonic stenosis, sub-
valvular aortic stenosis, patent ductus arteriosus, and
VSD.
7
Similar findings have been reported for dogs in
Europe, with variations including a high prevalence of
atrial septal defects in France and mitral valve dyspla-
sia in the United Kingdom and France. Although par-
ticular breeds can be predisposed as a group to certain
congenital malformations, the examiner must guard
Figure 2—Illustration depicting degree of importance and likely benefit of cardiovascular diagnostic testing in dogs and cats with
incidentally detected heart murmurs. As the features of a given case move from left to right in the 6 categories shown, the expected
importance and yield of diagnostic tests increase. *Examples of activities that could lead to cardiovascular stress include airplane travel
and general anesthesia.

JAVMA, Vol 246, No. 10, May 15, 2015 Vet Med Today: Reference Point 1079
against applying such generalizations too rigorously to
individual animals.
As mentioned for veterinary patients in general,
the examination is intended to differentiate pathologi-
cal from nonpathological murmurs, and in the case of
pathological murmurs, to narrow down the differential
diagnosis. Two common scenarios are described in the
following sections as practical examples.
Figure 3—Flow diagram of the general approach to evaluation of incidentally detected heart murmurs in dogs and cats. *Circumstances
in which echocardiography of a patient with a convincingly nonpathological murmur could be warranted include plans to breed the ani-
mal or a client’s desire to confirm or refute structural cardiac disease. †Tests should be selected on the basis of logistical limitations and
expected diagnostic yield. PMI = Point of maximal intensity.

1080 Vet Med Today: Reference Point JAVMA, Vol 246, No. 10, May 15, 2015
Scenario 1: A diagnostic evaluation beyond the
physical examination is indicated—Young dogs with
incidentally detected heart murmurs that warrant fur-
ther investigation include those with a continuous
murmur, a diastolic murmur, a murmur that obscures
the second (or both) heart sounds, a murmur accom-
panied by transient abnormal heart sounds (eg, a split
second heart sound), a murmur that radiates to the
carotid region, a systolic murmur best heard at the left
apex over the mitral valve area, or a murmur that is
best heard on the right hemithorax regardless of the
intensity grade of the murmur. In addition, further in-
vestigation is warranted for young dogs with systolic
murmurs of grade 3/6 or louder with a point of maxi-
mal intensity over the left heart base. Any murmur in
a dog that is directly related (eg, parent, offspring, or
sibling) to a dog with known congenital heart disease
warrants further investigation, even if the character-
istics of the murmur suggest it is a nonpathological
murmur, as is common in several breeds.
8,9,a
Addi-
tional indications for further evaluation include the
finding of a soft murmur in association with abnor-
mal pulsations or distension of jugular veins, abnor-
malities of the femoral arterial pulse (eg, bounding,
or hypokinetic and delayed [parvus et tardus] pulse),
evidence of poor peripheral perfusion, abnormalities
of mucous membrane color, or a cardiac arrhythmia
other than respiratory sinus arrhythmia.
Many young dogs with serious congenital heart de-
fects that have no obvious clinical signs will have easily rec-
ognizable abnormalities on ECG or thoracic radiographs.
Although these methods may offer useful ancillary infor-
mation, they cannot provide a definitive etiologic diagnosis
of the murmur. For example, in a study
10
to assess the use
of survey radiography for diagnosis of congenital cardiac
anomalies in dogs, the differential diagnoses included the
correct diagnosis for only 21 to 23 of 57 (37% to 40%)
dogs with congenital heart disease. For evaluation of young
dogs, the diagnostic yield of echocardiography is superior
to that of radiographic examination in that it is more likely
to provide information needed to identify a congenital heart
defect and enables the clinician to better assess disease se-
verity, the occurrence of multiple defects, and the suitability
of surgical or medical treatment, and to establish a more ac-
curate prognosis. Echocardiography should be performed
by a cardiologist for greatest accuracy.
11
The accuracy of
high-resolution Doppler echocardiography for the identifi-
cation of congenital heart defects is well established.
12
Scenario 2: A diagnostic evaluation beyond the
physical examination may or may not be indicated or
can be deferred—In a young dog, a grade 1/6 to 2/6,
short-duration, systolic heart murmur (eg, a midsystol-
ic murmur with clearly audible first and second heart
sounds) that is localized to the region of the left heart
base is typically nonpathological. Such a finding would
not necessarily indicate the need for diagnostic tests but
would warrant a discussion with the client regarding the
advisability of further evaluation. Considerations would
include complete identification and description of the
murmur’s characteristics, the breed of dog and its athleti-
cism or intended purpose (breeding, field trial, or other),
and the concerns and desires of the client (Figure 2).
With auscultation alone, it is difficult or impos-
sible to distinguish a nonpathological murmur from a
murmur with similar characteristics that is caused by a
trivial congenital lesion. This issue has little practical
importance in management of most dogs; a very mild
subaortic stenosis lesion, for example, would not be
expected to substantially impact the health of a given
patient. In a situation such as this, watchful waiting
can be a reasonable approach if additional features of
the case suggest that the importance of further diagnos-
tic testing will be low (Figure 2). However, such dogs
should not be bred until a definitive diagnosis is estab-
lished, which usually requires a complete echocardio-
graphic examination.
Heart Murmurs in Adult Dogs
Systolic murmurs are more common than diastolic
or continuous murmurs in adult dogs. Diastolic or con-
tinuous murmurs are invariably pathological and in all
cases should be investigated with echocardiography,
considering that these dogs can benefit from definitive
clinical diagnosis and treatment (eg, confirmation and
treatment of infective endocarditis or surgical or cathe-
ter-based closure of patent ductus arteriosus).
When a veterinarian detects a systolic murmur inci-
dentally, it is appropriate to seek a second opinion from
a cardiologist, who may make an assessment on the ba-
sis of auscultation or, if deemed necessary, echocardiog-
raphy. This approach may not be feasible for every pet
owner, however. A skilled veterinarian often can make a
provisional diagnosis on the basis of history and a physi-
cal examination that includes careful cardiac ausculta-
tion. For some clients and their pets, this approach can
be sufficient, whereas for others it might not be (Figure
2). Nonpathological systolic ejection murmurs (Appen-
dix 1) may be due to identifiable extracardiac disorders,
for which an in-depth cardiac evaluation is not needed.
When such a murmur is detected incidentally in adult
dogs and a plausible systemic cause is identified, the
evaluative approach can proceed as described in scenar-
io 2 for pediatric dogs with murmurs that may or may
not require further cardiovascular system testing. It is
expected that the murmur will resolve with normaliza-
tion of the systemic disturbance, and if not, cardiovas-
cular diagnostic testing should be performed.
Acoustic features of a murmur may further narrow
down the differential diagnosis at the time of ausculta-
tion. Ventricular septal defect and DMVD are examples
of disorders that cause so-called plateau-shaped sys-
tolic murmurs, which are named this way because of
their phonocardiographic appearance. Plateau-shaped
murmurs are recognized on auscultation by a similar
sound intensity throughout systole, and, typically, their
obliteration of the second heart sound. Conversely, sub-
aortic stenosis and pulmonic stenosis are examples of
disorders that cause systolic ejection murmurs. Ejection
murmurs have a crescendo (ie, increase in loudness dur-
ing systole) or crescendo-decrescendo (ie, loudest dur-
ing midsystole) character and do not typically interfere
with audibility of the second heart sound. In some adult
dogs, the sound intensity profile of a murmur—corre-
sponding to its phonocardiographic shape—can be dif-

JAVMA, Vol 246, No. 10, May 15, 2015 Vet Med Today: Reference Point 1081
ficult to discern on auscultation, making the auditory
distinction between plateau murmurs and ejection mur-
murs difficult. If auscultation results are ambiguous in
this respect, further diagnostic testing is justified.
The location of a murmur’s point of maximal inten-
sity also is helpful for identifying the likely cause of the
murmur. For example, an investigation
a
of the diagnos-
tic accuracy of auscultation for identification of mitral
regurgitation in Whippets revealed that auscultation of
any murmur was associated with very low specificity:
false-positive diagnoses of mitral regurgitation were
made for 166 of 186 (89%) dogs with murmurs. Partly,
this likely reflected the high prevalence of functional
left basilar murmurs in Whippets; indeed, when only
those murmurs heard over the left cardiac apex were
considered, indices of diagnostic accuracy substantially
improved and the frequency of false-positive diagnoses
decreased to 15 of 186 (8%).
a
Finally, murmur intensity, or loudness, is of some
limited benefit in determining severity of mitral valvu-
lar regurgitation in adult small-breed dogs with DMVD.
Overall, adult small-breed dogs typically have a larger
amount of mitral regurgitation if the murmur is louder
(corresponding to a higher grade).
13
This generaliza-
tion, however, cannot be used for providing a precise
prognosis for individual patients because body condi-
tion, orientation of the regurgitant jet, and sympathetic
activation may alter a murmur’s grade irrespective of
the severity of DMVD.
Some veterinary cardiologists deliberately auscult
adult dogs at rest and again immediately after exercise
as a means of identifying flow-dependent or heart rate–
associated murmurs. For example, whereas 68 of 100
(68%) auscultations in 19 Boxers revealed a murmur at
rest, 95 (95%) of auscultations of the same dogs revealed
a murmur after the dogs had 3 minutes of exercise in 1
study.
14
Furthermore, murmur intensity increased after
exercise; 2 of 100 (2%) murmurs were grade 3/6 with
exercise, compared with 0 (0%) at rest; 74 (74%) were
grade 2/6 after exercise, compared with 24 (24%) at rest;
and 19 (19%) were grade 1/6 after exercise, compared
with 44 (44%) at rest.
14
The practice of auscultation af-
ter physical exercise increases the rate of detection of
pathological murmurs and nonpathological murmurs.
14
Therefore, it may be considered when the veterinarian
and the client understand that the emergence of a new
murmur at a higher heart rate is not a conclusive find-
ing, but justification for additional diagnostic testing.
In an adult dog, systolic murmurs heard loudest
over the left cardiac apex are most commonly caused
by mitral regurgitation; in turn, the most frequent cause
of mitral regurgitation is DMVD, but DCM, infective
endocarditis, and congenital mitral valve dysplasia are
also recognized causes of mitral regurgitation. Systolic
murmurs heard best over the left heart base are man-
aged in adult dogs as described for puppies. Systolic
murmurs that are loudest over the right hemithorax are
most commonly caused by tricuspid valve regurgitation
(with or without pulmonary hypertension), subaortic
stenosis, or VSD, and further evaluation should be con-
sidered on the basis of concomitant factors (Figure 2).
In conjunction with the features of the murmur,
signalment profiling can be helpful. The simple process
of evaluating the murmur’s characteristics together with
the patient’s signalment narrows the differential diagno-
sis and helps the practitioner select appropriate diag-
nostic tests (Figures 4 and 5). This process is illustrated
with 2 examples.
Example 1: Evaluation of a small-breed (< 20 kg
[44 lb]) adult dog with a systolic murmur loudest over
the left apex—This type of murmur may be pathological
(eg, DMVD, mitral valve dysplasia, or infective endocar-
ditis of the mitral valve) or nonpathological (eg, anemia
or breed-associated or individual variation). Auscultatory
features of the murmur help make this distinction (Ap-
pendix 1), as do extracardiac observations (eg, pallor, sug-
gesting anemia) and the prevalence of specific disorders
in the patient’s breed. If uncertainty persists despite these
observations, or if the murmur is convincingly pathologi-
cal, additional investigation is justified (Figure 3).
Echocardiography provides a more precise and
more accurate diagnosis of the cause of a murmur than
does radiographic examination and is advised; however,
thoracic radiography often is performed first because of
lower cost, greater availability than echocardiography,
and ability to identify pulmonary and vascular abnor-
malities. Absence of radiographic evidence of cardio-
megaly in an adult dog with a systolic left apical mur-
mur suggests a nonpathological murmur, mild heart
disease (eg, early stage of DMVD), or heart disease
that may be clinically important but not yet associated
with cardiomegaly (eg, infective endocarditis). In adult
small-breed dogs with incidentally detected murmurs,
clinically important heart disease is uncommon if tho-
racic radiographic findings are normal. The decision to
pursue further diagnostic testing should be based on
assessment of all factors that pertain to the case (Fig-
ure 2). Echocardiography performed by a cardiologist
is the gold standard for identifying the cause of such
murmurs.
11
Assessment of circulating NT-proBNP con-
centrations provides additional information of limited
value in this situation; for example, in a study
15
of dogs
with preclinical DMVD, the median NT-proBNP con-
centration was significantly (P < 0.001) higher in dogs
with cardiomegaly than in those with a cardiac silhou-
ette of normal size.
However, the range of results was
broad, and many clinical results can be expected to fall
in a range of overlap between radiographically normal
heart size and cardiomegaly, conferring limited use for
clinical decision making for individual patients.
In adult small-breed dogs with incidentally detected
murmurs, serial follow-up of cardiac size on thoracic
radiographs can be a useful tool to monitor disease pro-
gression (Figure 4). For example, CKCS with DMVD
may have a VHS that is stable and may not have clinical
signs for years, followed by a rapid increase in VHS and,
eventually, the development of CHF. In a longitudinal
study of 94 CKCS with DMVD, the median VHS was 11
at 3.5 to 4 years, 11 at 2.5 to 3 years, 11.25 at 1.5 to 2
years, and 11.7 at 0.5 to 1 year before diagnosis of CHF;
at the onset of CHF, the median VHS had increased to
13.25.
16
Thus, in a typical case, an unchanging VHS of
10.6 to 11.3 in an adult CKCS with an incidentally iden-
tified left apical systolic murmur is unlikely to reflect ex-
tensive cardiac changes or imminent CHF.

1082 Vet Med Today: Reference Point JAVMA, Vol 246, No. 10, May 15, 2015
Example 2: Assessment of a large-breed (≥ 20 kg)
adult dog with a systolic murmur loudest over the
left apex—The causes of left apical systolic murmurs
in large-breed dogs are similar to those for small-breed
dogs. However, the prevalences of individual diseases in
the 2 populations generally are very different, and fewer
conclusions may be reached confidently on the basis of
physical examination results alone for large-breed dogs.
Indeed, differentiation between the principal causes of
left apical systolic murmurs in large-breed dogs via aus-
cultation alone is unreliable, and thoracic radiographs
may reveal few or no abnormalities in the early stages
of disease. Therefore, the single best diagnostic test for
evaluating an adult large-breed dog with an incidentally
discovered murmur is echocardiography (Figure 5).
Nonpathological murmurs must be considered
first, and their point of maximal intensity is rarely the
cardiac apex. If nonpathological murmurs are consid-
ered less likely on the basis of auscultatory features
(Appendix 1) and the rest of the physical examination
does not reveal a likely basis for a nonpathological mur-
mur, a pathological murmur is more likely and further
diagnostic testing is recommended. In adult large-breed
dogs, disorders that produce systolic murmurs that are
loudest over the left apex include DCM,
17
mitral valve
dysplasia, DMVD of large-breed dogs,
18
and infective
endocarditis. In large-breed dogs, DCM and DMVD
often produce soft, systolic, plateau-type murmurs, de-
spite a potentially aggressive disease course over time.
If the dog’s breed or other features suggest a particular
disorder, the differential diagnosis may be narrowed or
better prioritized, but not to the point of eliminating the
need for echocardiography in adult large-breed dogs.
Inevitably, the distinction between large- and
small-breed dogs involves overlap with dogs of an in-
termediate body size. It is also possible for small-breed
dogs to develop heart diseases that occur more com-
monly in large-breed dogs, and vice versa. Therefore,
the examples provided here should be considered to of-
fer general diagnostic approaches that need to be modi-
fied when individual variations are encountered.
Heart Murmurs in Geriatric Dogs
A geriatric animal is one that has entered the last
25% of the average expected lifespan for the species and
Figure 4—Flow diagram of a diagnostic testing approach for assessment of an adult small-breed (< 20 kg [44 lb]) dog with an incidentally
detected left apical systolic heart murmur and no overt signs of CHF. *Relevant conditions include chronic kidney disease, adrenal gland
disease, or diabetes mellitus. †Recommended for patients that have comorbidities or that are receiving treatment for CHF, cardiac ar-
rhythmias, myocardial systolic dysfunction, or any combination of these disorders. ABP = Arterial blood pressure measurement. SBA =
Serum biochemical analysis. UA = Urinalysis.

JAVMA, Vol 246, No. 10, May 15, 2015 Vet Med Today: Reference Point 1083
breed.
19
In this age group, murmurs due to congeni-
tal heart disease are identified occasionally,
20
but those
caused by adult-onset heart disease are much more
prevalent. Features of the cardiac auscultation and the
rest of the physical examination are at the core of an
accurate differential diagnosis. Characterization of the
murmur’s sound quality, point of maximal intensity, and
timing allow a skilled veterinarian to differentiate ini-
tially between findings suggestive of common disorders
versus those that suggest unusual disorders. For exam-
ple, a 10-year-old Dachshund with an incidentally de-
tected, grade 4/6 systolic left apical murmur most likely
has DMVD, but an otherwise similar dog with a grade
4/6 left basilar systolic murmur that radiates to the ca-
rotid region almost certainly has a disorder other than
DMVD. In each case, the veterinarian’s confidence in the
presumptive diagnosis helps guide the client’s decision
on whether to pursue diagnostic testing (Figure 2).
Geriatric small-breed dogs with murmurs common-
ly have DMVD, particularly if the murmur is systolic and
Figure 5—Flow diagram of a diagnostic testing approach for assessment of an adult large-breed (≥ 20 kg) dog with an incidentally
detected left apical systolic heart murmur and no overt signs of CHF. It should be noted that, in the absence of echocardiography, the
cause of most systolic murmurs in large-breed dogs cannot be determined definitively; thoracic radiography then becomes the most
important test to evaluate for cardiomegaly or evidence of CHF. Recommendations are provided for the most common causes of mur-
murs in adult dogs; others are possible but less prevalent. ‡In specific cases, measurement of analyte concentrations can be beneficial.
LA = Left atrium. Lab = Laboratory tests. T
4
= Thyroxine concentration. XR = Radiography. See Figure 4 for remainder of key.

1084 Vet Med Today: Reference Point JAVMA, Vol 246, No. 10, May 15, 2015
loudest over the left apex.
13,21
The demarcation between
adult and geriatric age groups must be considered indis-
tinct, and different breeds have characteristic prevalenc-
es of murmurs that span the adult and geriatric age cat-
egories. Results of 1 retrospective study
22
indicated that
a left apical systolic murmur develops in approximately
20% of each of the following dog breeds by these median
ages: CKCS by 4 years of age, Shih Tzus by 8.6 years
of age, Dachshunds by 9.5 years of age, Bichon Frisés
by 10.4 years of age, Miniature Poodles by 11.1 years
of age, Yorkshire Terriers by 12.7 years of age, and Lha-
sa Apsos by 13.2 years of age, with DMVD as the most
likely cause. Thus in geriatric dogs, or any adult dogs
of unknown age, signalment profiling is a useful tool in
developing and prioritizing differential diagnoses. This
process helps the veterinarian offer general guidance to a
client but does not replace the information provided by
thoracic radiography, echocardiography, or both.
In the absence of any other clinical signs possibly
related to heart disease, geriatric small-breed dogs with
systolic murmurs that have a point of maximal intensity
over the left apex can be evaluated by thoracic radiogra-
phy. As mentioned for adult small-breed dogs (example
1), thoracic radiographs can provide important prog-
nostic and therapeutic information for patients with
presumed or confirmed DMVD: a cardiac silhouette of
normal size and shape in a dog that has no overt signs
of decompensated heart disease is consistent with mild
DMVD, and no treatment currently available appears to
alter the progression of DMVD at this stage. Addition-
ally, such radiographs may then provide baseline infor-
mation for comparison as the disease progresses.
16
Echocardiography can provide clinically important
information about any geriatric dog with an inciden-
tally detected murmur. It is especially warranted if the
murmur has a point of maximal intensity over the right
hemithorax or is equally loud on the right and left sides
of the thorax; is loudest over the heart base; radiates
to the thoracic inlet, carotid arteries, or both; or is dia-
stolic or continuous. An echocardiogram is indicated
in a geriatric dog with a murmur that is accompanied
by a cardiac arrhythmia other than respiratory sinus
arrhythmia, distension or abnormal pulsations of the
jugular veins, or abnormalities of the femoral arterial
pulse. A murmur that is recent in onset and coexists
with vague systemic signs justifies diagnostic testing to
address the possibility of infective endocarditis.
A left apical systolic murmur might be detected in-
cidentally in a geriatric small-breed dog with signs the
client attributes to aging, including exercise intolerance
and decreased interaction with people, but such signs
can be caused by heart disease. In this instance, thoracic
radiographs and clinicopathologic tests (eg, CBC, serum
biochemical analysis, and urinalysis as appropriate) are
warranted; a radiographically normal cardiac size less-
ens the likelihood of a cardiogenic basis for the signs,
whereas cardiomegaly should prompt a recommenda-
tion for echocardiography to differentiate structural
heart disease from a large cardiac silhouette caused by
innocuous technical or individual animal factors.
In medium-, large-, and giant-breed geriatric dogs
with incidentally detected left apical systolic murmurs,
it is important to consider that the murmur may be
caused by such disorders as DMVD, which can progress
more rapidly in large- than in small-breed dogs; DCM;
or infective endocarditis. Therefore, in dogs that weigh
approximately 20 kg or more, a left apical systolic mur-
mur should prompt a recommendation for echocar-
diography as the initial diagnostic test of choice.
Heart murmurs that are convincingly nonpatho-
logical on the basis of a thorough auscultation are by
definition not caused by structural heart disease and
therefore do not require radiographic or echocardio-
graphic evaluation. As noted previously, it may be diffi-
cult to differentiate nonpathological murmurs from soft
pathological murmurs, and any uncertainty warrants
additional evaluation as appropriate for the signalment
of the patient; auscultation by a cardiologist or echo-
cardiography would be logical choices in this context.
Heart Murmurs in Kittens
The pediatric age group for cats can be considered
to include patients ≤ 6 months of age,
5
which is roughly
analogous to the pediatric population in human medi-
cine. In these young cats, the prevalence of congenital
heart disease has been estimated at 1.6% and 5% in adop-
tion centers and the referral setting, respectively.
23,b
It is
important to consider that young cats may have heart
diseases commonly recognized in adult cats (notably
hypertrophic cardiomyopathy), and that nonpathologi-
cal murmurs can occur in cats of any age.
23,b
In young cats, a nonpathological murmur may be
caused by systemic disturbances (eg, anemia) or iatro-
genic factors (eg, excitement) or can be detected in pa-
tients with no identifiable systemic or structural cardio-
vascular disorder.
b
Murmurs attributable to anemia may
be somewhat easier to recognize in young cats because
they often have a Hct that is below laboratory reference
intervals for adult cats and have a thin chest wall. These
murmurs are high-frequency, mid-systolic (whereby
the first and second heart sounds still are heard clearly),
and often soft and variable in their intensity depending
on the severity of the anemia but seldom of grade > 2/6.
They often are best heard at the left heart base or apex.
Concurrent findings of pallor or other physical abnor-
malities should be evaluated because the murmur, in
such instances, might be only 1 indicator of a systemic
disturbance.
The specific characteristics that separate patho-
logical and nonpathological murmurs fail to reliably
do so in most cats with grade 1/6 to 3/6 systolic mur-
murs. This uncertainty can be addressed with 1 of 3 ap-
proaches: further cardiovascular diagnostic testing, (eg,
Doppler echocardiography), second-opinion auscul-
tation by a cardiologist, or simple reexamination and
reauscultation, typically after a period of 2 to 4 weeks.
A pediatric stethoscope is often helpful for accurate
auscultation of kittens and small cats. The course to be
pursued should be decided on the basis of perceived ad-
vantages and liabilities of each approach and is a matter
for discussion between the veterinarian and the client
according to several important criteria (Figure 2). A
persistent, soft, left parasternal murmur may be either
pathological or nonpathological, and this distinction
is best made by Doppler echocardiography. As another
example, there is a greater incentive to obtain an echo-
cardiographic diagnosis when a murmur is detected in-

JAVMA, Vol 246, No. 10, May 15, 2015 Vet Med Today: Reference Point 1085
cidentally in a young cat that is a member of a breeding
colony or is scheduled to undergo general anesthesia,
to assist with breeding decisions and anesthetic plan-
ning, respectively.
When young cats have incidentally detected mur-
murs with clearly pathological characteristics (Appen-
dix 1), diagnostic testing is warranted. Except for most
cases of patent ductus arteriosus in cats with normal
pulmonary artery pressures, where a continuous mur-
mur is evident,
c
congenital cardiac malformations in
cats generally produce a systolic murmur. Murmur in-
tensity and location, while helpful for narrowing the
differential diagnosis list, have limited value regarding
specific diagnosis and prognosis in cats. Cats with clini-
cally unimportant VSDs routinely have loud (eg, grade
5/6) systolic murmurs, and murmur intensity cannot
be used for judging lesion severity. In this age group,
2-D and Doppler echocardiography by a cardiologist
are recommended for diagnosis and prognosis because
they are the most effective means of identifying the le-
sion and its degree of severity, concurrent defects, risk
of complications, need and options for corrective treat-
ment, and broad prognosis. Thoracic radiographs are of
value, and a cardiac silhouette of normal size, in the ab-
sence of evidence of pulmonary abnormalities, provides
some reassurance that severe congenital heart disease is
unlikely. However, assessment of cardiac size on tho-
racic radiographs in young cats can have limited accu-
racy; structural heart disease can be wrongly suspected
if peritoneopericardial diaphragmatic hernia causes a
large cardiac silhouette in a cat with a normal heart, and
conversely, it may be missed if the murmur is caused by
a congenital malformation that causes concentric ven-
tricular hypertrophy.
Heart Murmurs in Adult and Geriatric Cats
Systolic murmurs are common in overtly healthy
adult cats and have been reported to affect 16 of 103
(16%) to 44 of 100 (44%) cats ausculted by veterinar-
ians in hospital and shelter settings.
24–26,d
The frequency
of murmur detection appears to increase with repeated
examinations
26
and with stimulation of the cat.
25
Among adult cats with incidentally detected mur-
murs but no overt clinical signs, the prevalence of heart
disease has been reported as 16 of 103 (16%) to 44 of
57 (77%), varying by geographic location, examiners,
and study methods.
24–29
The most common underly-
ing heart disease in adult cats is hypertrophic cardiomy-
opathy (found in 15/103 [15%] to 38/61 [62%] of adult
cats with incidentally detected murmurs), and the most
common nonpathological murmur is caused by dynamic
right ventricular outflow tract obstruction (8/103 [8%]
to 9/57 [16%] of adult cats with incidentally detected
murmurs).
24–30,e
Subjectively, there is extensive overlap be-
tween the auscultatory characteristics of murmurs caused
by cardiomyopathy and those resulting from nonpatho-
logical murmurs in cats, and generally, these cannot be
differentiated from each other by auscultation alone. Aus-
cultation of other cardiac abnormalities such as a gallop
sound or arrhythmia might be even more valuable than
the detection of a murmur for identifying cats at increased
risk for CHF or arterial thromboembolism.
31
Clients might not recognize clinical signs initial-
ly, but a veterinarian can detect extracardiac physical
findings that suggest a systemic disorder, and a client
could then realize retrospectively that clinical signs
were present after they have resolved with treatment.
This scenario is particularly relevant for geriatric cats,
in which hyperthyroidism, other disorders causing sys-
temic hypertension, and anemia are more prevalent
than in younger cats and can cause a nonpathological
murmur that resolves with identification and treatment
of the underlying disorder (Figure 6).
Before auscultation, important features of the physi-
cal examination include precordial palpation, because an
increase in the force of the cardiac beat at the apex can
occur with cardiomegaly or with diseases such as hyper-
thyroidism that are associated with high cardiac output,
and a thrill indicates a murmur grade ≥ 5/6; mucous
membrane color, because pallor could suggest anemia as
the cause of a murmur; evaluation of the neck for jugular
distension and the abdomen for ascites, both of which
are very uncommon in overtly healthy cats; and pulse
quality, which is highly variable in cats.
A systematic evaluation of the murmur’s character-
istics is indicated when a heart murmur is detected in a
cat. The small size of the heart in cats can make specific
distinctions between sounds with greatest intensity at the
apex or base challenging in some; a common oversight
is failure to auscult parasternally and over the sternum
specifically. In cats, murmurs are often labile, changing
in intensity with excitement or heart rate, or simply in-
creasing or decreasing in intensity over time.
25,26,d
This
finding has little diagnostic value because it may occur
with pathological or nonpathological murmurs.
25
Later-
alization can narrow the differential diagnosis list in some
patients. For example, right-sided systolic murmurs in
adult cats are more commonly caused by dynamic right
ventricular outflow tract obstruction, hypertrophic ob-
structive cardiomyopathy, or congenital malformations
(notably tricuspid dysplasia and VSD).
Thoracic radiography can be helpful for detection
of advanced cardiac disorders: a VHS > 9.3 in cats is
strongly associated with cardiac disease as a cause for
dyspnea.
32
However, in cats with incidentally detected
murmurs (where clinical signs are absent by definition),
a higher rate of false-negative results could be expected
than for cats with signs referable to the cardiovascular
system. Measurement of circulating NT-proBNP concen-
tration also has value for detection of occult cardiomy-
opathy; in 1 study,
33
a result < 50 pmol/L indicated car-
diomyopathy was very unlikely, whereas a result > 100
pmol/L suggested cardiomyopathy was present.Thoracic
radiography, NT-proBNP testing, or both may be useful
when client limitations (financial, logistic, geographic, or
other) prevent the cat from undergoing complete 2-D and
Doppler echocardiography (Figure 6). Echocardiography
is considered the diagnostic test of choice for pinpointing
the cause of a murmur. Furthermore, echocardiography
was found to have superior results, compared with radi-
ography (28% to 72% accuracy) or ECG (12% to 60%
accuracy) for identifying left atrial enlargement in cats,
34
and left atrial enlargement is probably the most impor-
tant risk factor for adverse cardiac events and shortened
survival among many types of heart diseases of cats.
31,35

1086 Vet Med Today: Reference Point JAVMA, Vol 246, No. 10, May 15, 2015
Areas of Uncertainty
Many aspects of heart murmur assessment deserve
greater attention. The following specific areas represent
points that are especially relevant to a clinical setting.
Overlap between healthy animals with nonpatho-
logical murmurs and animals with mild forms of heart
disease—It can be challenging even for experienced car-
diologists to differentiate healthy animals with nonpatho-
logical heart murmurs from those with mild outflow
tract obstruction or other subtle structural heart lesions.
Breed-associated overlap between physiologic variants
and pathological lesions has been investigated in Boxers,
Whippets, and other breeds.
8,9,a
It may not be important
to differentiate functional murmurs from murmurs asso-
ciated with mild forms of heart disease in pet animals, as
their management will be similar. It can be more impor-
Figure 6—Flow diagram depicting a general diagnostic testing approach for assessment of an adult (> 6 months of age) cat with an
incidentally detected heart murmur. Dashed lines indicate areas of investigation or controversy where several approaches are possible.
*Echocardiography may still be considered if other features support it. †Circulating concentration (pmol/L). RI = Reference interval. See
Figures 4 and 5 for remainder of key.

JAVMA, Vol 246, No. 10, May 15, 2015 Vet Med Today: Reference Point 1087
tant to make this distinction in breeding animals, how-
ever, because an affected animal may have clinically un-
important heart disease but be capable of transmitting a
predisposition to developing heart disease to its progeny.
Integration and value of newer diagnostic tests—
Diagnostic tests of blood, serum, or plasma (eg, circulat-
ing concentrations of biomarkers for cardiac disease) of-
fer the promise of information obtained without requir-
ing referral for echocardiographic evaluation, although
the cause of a heart murmur cannot be concluded from
evaluation of bloodborne cardiac biomarkers alone. In-
vestigations of such assays in large series of animals with
similar murmurs would be useful; for example, differ-
ences may be detectable between dogs with pathological
murmurs and dogs with nonpathological murmurs of
similar intensity and character. Furthermore, assessment
of the role of circulating biomarker assays as one of mul-
tiple components of a diagnostic evaluation (eg, assess-
ment of thoracic radiographs and serum biomarker con-
centrations together, compared with echocardiographic
examination) in dogs or cats with incidentally detected
murmurs could be of clinical benefit.
Outcome evaluation—The authors are aware of no
specific studies that describe the long-term outcomes of
dogs or cats that underwent diagnostic evaluation of in-
cidentally detected heart murmurs, compared with those
in which murmurs were not evaluated further. Neverthe-
less, it is self-evident that failure to diagnose the cause of
a murmur can sometimes lead to a worse outcome. In 1
retrospective study,
36
dogs with severe pulmonic stenosis
that did not undergo balloon-valve dilation had a worse
outcome than those that did; the same results have been
found for dogs with corrected versus uncorrected patent
ductus arteriosus in multiple studies.
37,38
Failure to iden-
tify advanced cardiac disease prior to general anesthesia
or IV fluid therapy can result in unexpected signs of CHF.
Conversely, failure to identify a murmur as nonpathologi-
cal (and therefore clinically benign) can lead to needless
owner anxiety and an unjustifiably guarded prognosis.
Whether the benefit of diagnosing the cause of a
murmur is distributed equally across different diseases,
species and breeds, and murmur types is not known.
Similarly, many other important questions remain, in-
cluding which subgroups of patients receive the great-
est long-term benefit from diagnostic testing, the rec-
ommended interval and methods for follow-up, and the
costs and benefits of reevaluation at various intervals.
Conclusions
It is easy to recommend that all patients with inciden-
tally detected heart murmurs undergo echocardiography.
A true understanding of the realities and imperatives of
clinical practice says otherwise. This report is intended to
provide a summary of the patient-, client-, and veterinarian-
based factors that can help attending veterinarians recom-
mend whether or not to pursue further diagnostic evalua-
tion of patients with incidentally detected murmurs and the
advantages and suitability of various diagnostic approaches.
f
a. Stepien RL, Kellihan H, Luis Fuentes V. Accuracy of ausculta-
tion alone to identify mitral insufficiency in adult Whippets
(abstr). J Vet Intern Med 2011;25:1480.
b. Dirven MJM, Barendse MA, vanMook MC, et al. Prevalence of
heart murmurs and congenital heart disease in 2935 young cats
(abstr). J Vet Intern Med 2012;26:1513.
c. Hitchcock LS, Lehmkuhl LB, Bonagura JD. Patent ductus arte-
riosus in cats: 21 cases (abstr). J Vet Intern Med 2000;14:338.
d. Drourr LT, Gordon SG, Roland RM, et al. Prevalence of heart
murmurs and occult heart disease in apparently healthy adult
cats (abstr), in Proceedings. 28th Annu Am Coll Vet Intern Med
Forum 2010. Available at www.vin.com/doc/?id=4504365. Ac-
cessed Apr 20, 2014.
e. Allen JW, Yee K, Buckner MH, et al. NT-proBNP levels in 30 cats
with dynamic right ventricular outflow obstruction (abstr). J Vet
Intern Med 2010;24:695.
f. An executive summary for veterinarians on incidentally de-
tected heart murmurs in dogs and cats and a client information
sheet are posted with the article at avmajournals.avma.org.
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1088 Vet Med Today: Reference Point JAVMA, Vol 246, No. 10, May 15, 2015
Appendix 1
Criteria for helping differentiate nonpathological from pathological heart murmurs in dogs and cats.
Appendix 2
Heart murmur grading scale.
Grade Features of cardiac auscultation and palpation
1/6 Nearly imperceptible, may be heard with very careful auscultation in a quiet environment; always focal
2/6 Heard readily but very soft; always focal
3/6 Heard readily, moderate intensity; usually regional (can be heard in several auscultatory regions of the heart)
4/6 Heard readily, loud, and usually radiates widely (can be heard in most or all auscultatory regions of the heart), but without a
palpable thrill
5/6 Heard readily, loud, and associated with a precordial thrill, but the murmur is not heard with the stethoscope lifted off the surface
of the thorax
6/6 Heard readily, loud, associated with a precordial thrill, and the murmur remains audible with the stethoscope lifted 1 cm off the
surface of the thorax
(Modified from Ettinger SJ, Suter PF. Heart sounds and phonocardiography. In: Canine cardiology. St Louis: Saunders-Elsevier, 1970;12–39.
Reprinted with permission.)
Descriptor A nonpathological murmur is more likely A pathological murmur is more likely
Sensitive The murmur is absent or much softer at rest than with The murmur is present at rest or with activity; it can be
excitement or exercise; it changes with position or heard at all times
phase of respiration
Short The murmur is of short duration, predominantly heard in The murmur remains loud through most of systole
early or midsystole
Single There are no other associated abnormal heart sounds or Additional auscultatory abnormalities are present, there
physical examination abnormalities; no clicks, gallops, are other abnormalities on physical examination, or both
or arrhythmias are heard
Small The murmur is localized to the left heart base or to 1 location; The murmur radiates from the point of maximal intensity
it does not radiate
Soft The murmur is soft or quiet; generally grade 1/6 or 2/6 The murmur is loud (ie, grade 3/6 or louder)
Systolic The murmur duration is limited to midsystole The murmur is continuous or a diastolic component
is also audible
Evaluation of murmurs with the 6-S rubric can be a useful means to help determine the need for additional diagnostic testing. It is imortant
to note that pathological murmurs may, if caused by lesions that generate minimal turbulence, be mistaken for nonpathological murmurs. (Modi-
fied from Bronzetti G, Corzani A. The seven “S” murmurs: an alliteration about innocent murmurs in cardiac auscultation. Clin Pediatr (Phila)
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