Thirty-six cases of heart attack or sudden death in marathon runners have been reported in the world literature to date. The mean age of the runners was 43.8 yr (range = 18 to 70), the mean years' running was 6.8 yr (range = 0.5 to 29), and the mean best standard 42.2 km marathon time was 3 h 28 min (range = 2 h 33 min to 4 h 28 min). Coronary artery disease was diagnosed either clinically, angiographically, or at autopsy in 27 runners (75%), two of whom also had histological evidence of hypertrophic cardiomyopathy. Seventy-one percent of the runners with coronary artery disease had premonitory symptoms, and most ignored such symptoms and continued to train or race. Fifty percent of all cardiac events occurred either during or within 24 h of competitive running events or long training runs. The marathon running population does not constitute solely persons with excellent cardiovascular health. Marathon runners, especially those with a family history of heart disease and other coronary risk factors, should not consider themselves immune to either sudden death or to coronary heart disease and should seek medical advice immediately if they develop any symptoms suggestive of ischemic heart disease. Physicians should not assume that "physically fit" marathon runners cannot have serious, life-threatening cardiac disease.