We studied 56 children echocardiographically, ages four to 15 years (mean nine years) with acute rheumatic fever to determine the extent of cardiac involvement. All had a clinical diagnosis of carditis. Mitral regurgitation was always present and was associated with aortic regurgitation in 53.6% and tricuspid regurgitation in 32.1%. Mitral valvar prolapse was observed in 18 patients 5(32.1%) and could not be differentiated from myxomatous prolapse in 10 (17.8%). Cordal rupture was detected in seven patients (12.5%), three of whom required surgical treatment. Other findings concerning the mitral valve were vegetations in two patients (3.6%), commissural fusion without stenosis in 36(64.3%), and mitral stenosis in four (7.1%). Heart failure was usually secondary to valvitis rather than myocarditis, and led to surgical treatment in seven patients. The myocardial function was depressed in only two patients. In both, the ejection function returned to normal after medical treatment. Echocardiography provides important information on the involvement of the heart in acute rheumatic fever, helping to determine prognosis and the results of treatment.