M-mode, cross-sectional and color flow Doppler echocardiography were performed in 28 patients with acute rheumatic fever. The patients were grouped according to the presence or absence of carditis and congestive heart failure. Abnormal echocardiographic findings were found in 25 patients (89%), including five with no carditis. M mode echocardiography showed significant cardiac enlargement in all patients with carditis, and in two patients with no carditis. The myocardial contractility, as based on ejection fraction and fractional shortening, was normal in all patients except one. Prolapse of the leaflets of the mitral valve (57%) and increased echogenicity of the leaflets of the mitral valve (36%) were the most common findings seen on cross-sectional echocardiography. Pericardial effusion was seen in six patients (21%), all with heart failure. Color flow and Doppler echocardiography showed that mitral regurgitation, which was seen in 24 patients (86%), was the most common finding. Aortic regurgitation was found in 17 patients (60%). The presence of congestive heart failure in patients with carditis was related to the severity of the valvar regurgitation and the number of valves involved. Echocardiographic evidence of rheumatic involvement of the heart may be observed even in the absence of clinical signs of carditis.