A study of 3 necropsy-proved cases of single ventricle (cor triloculare biatriatum) with pulmonary stenosis and normally related great vessels is reported. Clinically, 2 of these cases were considered to be examples of the tetralogy of Fallot. In the third case, a right-to-left shunt at atrial level caused by tricuspid stenosis led to a diagnosis of tricuspid atresia. Analysis of the electrocardiograms, which were available in 2 of the cases, revealed no leads that could be classed as specific for single ventricle with normally related great vessels. This study indicates the difficulty in distinguishing cor triloculare biatriatum with pulmonary stenosis and normally related great vessels from the tetralogy of Fallot and, at times, from tricuspid atresia.