Increasing experience with surgical palliation concluding in a Fontan-type operation has led to re-examination of the morphology of the hypoplastic left heart syndrome. It is evident that aortic atresia is not synonymous with the hypoplasia of the left heart and 5-7% of patients with aortic atresia will have a muscular-outlet ventricular septal defect reflecting infundibular septal displacement with a normal mitral valve and left ventricle. Such patients may be candidates for a biventricular repair. Amongst those patients with aortic atresia or stenosis and gross underdevelopment of the left heart with either mitral stenosis or atresia, less than 5% will exhibit structural abnormalities of the pulmonary or tricuspid valves or pulmonary arteries or anomalies of pulmonary venous connections precluding application of a Fontan algorithm. Ventriculo-coronary connections have been observed in the subepicardial coronary vessels of babies with the hypoplastic left heart syndrome, but they are usually less egregious than those connections occurring in the setting of the pulmonary atresia and intact ventricular septum. Finally, coarctation of the aorta is an integral component of the hypoplastic left heart syndrome.