Atrial fibrillation (AF) is a common arrhythmia, occurring in 0.4% of the general population. AF has been shown to be associated with left atrial enlargement, which is considered both a cause and a consequence of the arrhythmia. The aim of the study was to determine the influence of AF on changes in echocardiographically determined left atrial (LA) size, during 5 year follow-up period, in a population with well-controlled hypertension, free from structural heart disease, except mild left ventricle thickening, and with an absence of other potential causes of atrial enlargement. The study group, comprised of 81 patients with persistent AF, with underlying hypertensive heart disease, consecutively referred for elective direct current cardioversion. The mean age of the study population was 59.3+/-8.4 years (ranged from 43 to 80), a mean AF duration was 8.8+/-8.7 months (ranged from 1 to 30 months). The patients underwent two-dimensional echocardiography to determine left atrial size, before and 5 years after cardioversion. Twenty out of eighty-one cardioverted patients maintained sinus rhythm 5 years after cardioversion (25%). In this group anteroposterior LA dimension and LA volume decreased from a mean (+/-S.D.) 49.7+/-4.5 to 46.8+/-4.8 mm (-6%, p < 0.05) and from 103.6+/-28.8 to 91.1+/-18.3 cm2 (-9.2%, p < 0.05), respectively. Left ventricle ejection fraction increased from 52.8+/-6.3% to 60.0+/-4.0% (p < 0.05) and clinical stage improved in patients who maintained sinus rhythm through 5 years. In contrast, in the AF group, anteroposterior LA dimension and LA volume increased from 46.6+/-4.3 to 48.1+/-5.6 mm, and from 91.3+/-20 to 103+/-34 cm2 (by an average 3.3% and 14.3%, respectively), at the end of study. When divided into two groups: Imid R:II and III NYHA class, in AF patients LA volume increased by an 21.4% in the III NYHA class and 7.3% in the Imid R:II NYHA class. Left ventricular ejection fraction did not change between the two echocardiographic studies in the AF group (44.9+/-14.3% vs. 44.6+/-12.9%, Ns). In conclusion, it has been proved that AF occurring in patients with hypertensive heart disease causes a slow and progressive increase in LA size especially in patients in functional III NYHA class, and that the maintenance of sinus rhythm partially reverts the process of LA enlargement in patients with well-controlled hypertension, a history of AF and successfully treated for AF.