Abstract An instance is recorded, in a male infant dying at the age of three months, of an abnormal origin of the left coronary artery from the pulmonary artery, associated with marked enlargement of the heart (due to hypertrophy and dilatation of the left ventricle), together with extensive degenerative changes in the ventricular wall supplied by the malposed vessel. In view of these findings, it is probable that the paroxysmal attacks of acute discomfort precipitated by exertion and associated with profound vasomotor collapse occurring in this infant were those of angina pectoris. The electrocardiographic picture in our case was similar to that seen in adults with important coronary disease. In the few recorded cases (8 in number in addition to our own) of this rare anomaly a characteristic pathological picture has resulted. Death within the first year has been the rule. Two of the cases have been exceptional. A review of congenital variations in the coronary vessels and a discussion of their embryological background are included. A bibliography is appended.