Two-dimensional echocardiography has proved its utility in the diagnosis of cor triatriatum sinister by visualizing the defect and its relation to the other structures. Recently pulsed and continuous wave Doppler have been used to determine the degree of obstruction of the membrane. In this study we present three patients with ages six, eight and fourteen months respectively, all with a clinical history of growth retardation, respiratory infections and dyspnea. The patients were studied with two-dimensional and color flow Doppler echocardiography. In all, a membrane was visualized, which divided the left atrium in two chambers, a superior one which received the pulmonary veins and an inferior in continuity with the mitral valve and the left atrial appendage and with color flow Doppler the absence of obstruction at this level was demonstrated. In one patient besides the anomaly of cor triatriatum complete transposition of great arteries with pulmonary stenosis was diagnosed and in another one, patent ductus arteriosus and ventricular septal defect. Diagnosis were confirmed by hemodynamic studies. It is concluded that the color flow Doppler is a diagnostic method of great utility because it permits to obtain more information which complements conventional echocardiography.