Ectopic origin of a coronary artery from the aorta is uncommon. In the last decade, its importance as a possible cause of sudden death has been documented. Initially, only the left coronary artery was implicated. Lately, the ectopically arising right coronary artery has also been shown to be involved in cases of sudden death. We reviewed the pathologic anatomy in 23 cases of ectopic origin of a coronary artery from the aorta. In three of these cases, death could be attributed to ectopic origin of a coronary artery. In one case the left coronary artery arose from the right aortic sinus, and in two cases the right coronary artery arose from the left aortic sinus. In one of these, a scar of healed myocardial infarction was present in the inferior wall of the left ventricle. The possible mechanism for sudden death in these cases is reviewed and emphasis placed on the theory that the acute angle at which the ectopic artery leaves the aorta results in a flap-like mechanism at the arterial ostium. Ostial stenosis by the flap could be a significant factor in causing myocardial ischemia in some patients and also in sudden death.