The congenital anomaly in which the left coronary artery arises from the main pulmonary artery is infrequent, but lethal, and since it can be alleviated surgically, its recognition and hemodynamic consequences are important. On the basis of 140 reported cases and our seven cases, it seems to present in one of four ways: (1) in infancy with angina-like symptoms or as cardiomyopathy, and later (2) as mitral insufficiency, (3) continuous murmur, or in adults (4) by sudden death. Visualization of the coronary arteries provides the definitive diagnosis, and the problem is the selection for this procedure. The electrocardiogram, the most helpful laboratory aid, is diagnostic of infarction in 80% of the infant group; in the remainder other forms of cardiomyopathy may be confused. Although blood flows directly into the pulmonary artery in the majority of cases, it flows in the reverse direction in a few and this must be determined preoperatively. Some unanswered questions are the subject of discussion: Why the majority of infants have onset of symptoms at about 8 weeks of age, and why some survive to childhood and adult life. The pathological findings are reviewed. Although the greatest surgical therapy experience has been with obliteration of the anomalous left coronary artery (ALCA) at its connection with the pulmonary artery, anastomosis between aorta and ALCA provides an additive supply for both the present and the future.