Eight patients with single ventricle were studied echocardiographically. In six, the ventricular septum was not detectable; in two, a septal-like bulboventricular ridge was identified. Two atrioventricular (A-V) valves were found in all patients; in six, both valves were identified simultaneously with the transducer held stationary along the left sternal edge. Dextro-transposition of the great arteries was noted in three patients. The echocardiogram of one of four patients with levotransposition of the great arteries was consistent with later proved left A-V valve stenosis associated with Ebstein's malformation. Mitral-semilunar valve continuity was presented in five cases. Echocardiographically, the absence of the ventricular septum in a patient with two A-V valves make a diagnosis of single ventricle likely. The presence of ventricular septal-like echoes does not exclude the diagnosis of single ventricle since the right ventricular infundibulum may remain as a small outlet chamber separated from the left ventricle by an eccentric bulboventricular ridge.