Congenital coronary artery anomalies have been associated with sudden death. Twenty-two patients who were victims of sudden death (mean age 46) and who had no significant anatomic cause of death were examined at autopsy and compared with 19 patients who died of known causes (control group). The hearts of these 41 patients were examined for abnormalities of acute angle takeoff of the coronary artery and presence of ostial valve-like ridges. Of the 22 patients who died suddenly, 13 (59%) had acute angle takeoff of the coronary artery and 9 (41%) had ostial valve-like ridges. Of the 19 control subjects, 4 (21%) had acute angle takeoff and only 2 (11%) had an ostial valve-like ridge. The difference was statistically significant (p = 0.015 and 0.031, respectively). It is suggested that aortic root dilation may compress coronary arteries with acute angle takeoff and that ostial valve-like ridges may act as occlusion valves. Thus, either may cause acute obstruction of the proximal coronary artery and lead to sudden death. A very lethal combination for sudden death would be the presence of severe coronary artery disease, an acute angle takeoff and an ostial valve-like ridge.