Heart failure is a growing health problem in western societies. A significant number of patients with heart failure may need in-hospital treatment. The aim of this study was to compare the epidemiology, treatment and prognosis of inhospital heart failure at Landspitalinn during the years 1986 and 1996 respectively. Landspitalinn is one of two major hospitals in Reykjavik. Methods: We investigated hospital files for all patients discharged with the diagnosis of heart failure (based on ICD IX) from the Department of Medicine during the years 1986 and 1996 respectively. Results: Heart failure was diagnosed in 112 admissions among 82 patients (44 female, 38 male) in 1986, and in 207 admissions among 165 patients (71 female, 94 male) in 1996. Taking into account the total number of admissions to the Department of Medicine, the relative contribution of heart failure was 1.84% in 1986 and 3.66% in 1996 (pO.05). The mean age of all patients was 76.5 among women and 73.6 among men (p<0.05), hut there was no significant age difference between 1986 and 1996. The number of in-hospital deaths was 13 in 1986 (16%) and 31 in 1996 (19%). The mean age of the patients who died in hospital was 79.8 years but 73.9 years among those who survived the hospital stay (PO.05). On december 31st 1987, 35 (43%) of those diagnosed in 1986 were dead and on december 31st 1997, 77 (47%) of those diagnosed in 1996 were dead. Ischémie heart disease was the most common cause of heart failure, 52% and 64% of all cases were due to ischémie heart disease in women and men respectively (p=0.06). Hypertension, idiopathic dilated cardiomyopathy and heart valve disease were less common. The use of ACE blockers increased from 26% in 1986 to 55% in 1996. Otherwise there were no significant differences in medication given between the two years (diuretics 96%, digitalis 51 %, beta blockers 24%, calcium channel blockers 16%, long acting nitrates 35%, warfarin ordicumarol 16%) Conclusion: The incidence of in-hospital heart failure increased from 1986 to 1996. This may reflect an increased prevalence of heart failure in the society as well as an increased awareness of health professionals for the disorder. Women with heart failure in hospital are generally older than men. Ischémie heart disease is the most common underlying heart disease and appears to be somewhat more common in men than women. Apart from the increased use of ACE inhibitors there were no major changes in the medical treatment of heart failure between 1986 and 1996. The long-term prognosis for patients diagnosed with in-hospital heart failure is poor. Considering the high mortality and morbidity, treatment and prevention of this disorder remains a major challenge.