Sudden death among military recruits is rare; it occurred in only 126 of 6.3 million recruits who entered basic training during this 25-year period. Of the 126 sudden deaths, 108 occurred during exercise. Just over half of the recruits who died (64 of 126) had a heart abnormality identified at autopsy. The most common heart abnormalities involved the coronary arteries; in one of these conditions, people are born with an abnormally located left coronary artery. The second most common heart condition was myocarditis, an inflammation of the heart muscle. The third most common heart condition was hypertrophic cardiomyopathy, a condition in which people are born with an abnormally enlarged muscular wall of the heart that can block normal blood flow during heavy exercise. In 44 of the 126 recruits who died, examination of medical records and autopsy results revealed no explanation for the death. Other causes of death included sickle-cell crisis (3 deaths), blood clot to the lung (2 deaths), internal bleeding (1 death), bleeding into the brain (5 deaths), asthma or other lung disease (4 deaths), and heat stroke (3 deaths).