The causes of sudden, unexpected death in highly-conditioned competitive 
athletes are summarized. In the vast majority of young athletes (less than 35 
years of age) sudden death is due to underlying structural cardiovascular 
disease. Hypertrophic cardiomyopathy appears to be the most common cause of such 
deaths and may account for about one-half of the sudden deaths in a youthful 
athletic population. Cardiovascular abnormalities that appear to be less 
frequent important causes of sudden death include anomalous origin of the left 
coronary artery from the anterior sinus of Valsalva, ruptured aorta (due to 
cystic medial necrosis), idiopathic concentric left ventricular hypertrophy and 
coronary artery atherosclerosis. Other diseases which are probably particularly 
uncommon causes of sudden death in the young athlete include mitral valve 
prolapse, aortic valvular stenosis, acute myocarditis, QT interval prolongation 
syndromes, hypoplasia of the coronary arteries or sarcoidosis. Cardiovascular 
disease in young athletes is usually unsuspected during life. In only about 25% 
of those competitive athletes who die suddenly is underlying disease identified 
prior to participation and rarely is the correct clinical diagnosis made. In 
contrast, when sudden death occurs in older competitive or recreational athletes 
(over 35 years of age) it is usually due to coronary artery disease.