A rare form of common ventricle with normally related great vessels and normal tricuspid and mitral valves should be considered in the differential diagnosis of cardiac anomalies presenting with cyanosis. Fourteen cases of this type of common ventricle were studied; in 7 the diagnosis was made at necropsy and in 7 it was based on angiographic evidence. That the common ventricle was morphologically a left ventricle was determined in the 7 necropsy cases, and angiocardiographic examination confirmed the findings in the others. Continuity of the aortic valve and the mitral valve was observed in all the necropsy cases and in 5 of the clinical cases. Cyanosis had been observed clinically in 13 of the 14 cases, and pulmonary stenosis was present in 4 necropsy and 3 clinical cases. Electrocardiograms showed left axis deviation in 9 of the 13 cases studied. Vectorcardiographic findings, though variable and available in only 7 cases, tended to show a narrow horizontal plane QRS vector loop in patients with restricted pulmonary blood flow and a wide loop in those with increased pulmonary flow. The clinical, laboratory, and pathologic findings are reported and the differential diagnosis and the profile of the condition are considered.