In complete transposition of the great vessels the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. There are thus two closed circulations: in one the systemic blood enters the right heart from the vena cava and returns directly to the systemic circulation once more through the aorta; in the other the pulmonary blood enters the left heart via the pulmonary veins and is recircuited through the lungs by way of the pulmonary artery. Without additional anomalies, this malformation would obviously be incompatible with life. But other anomalies, such as an interauricular septal defect, a patent foramen ovale, an interventricular septal defect, or a patent ductus arteriosus are almost invariably present. In their absence or with their closure, death must follow. The fact that relative longevity in patients with transposition is associated with interventricular septal defects or multiple shunt pathways was stressed by Hanlon and Blalock, in 1947, in an analysis of 123 proved...