Exercise, the athlete's heart, and sudden cardiac death.

Physical activity is a potent therapy for both the prevention and treatment of cardiovascular disease. Exercise appears to most benefit people who are the least active. There is some evidence to suggest that a curvilinear relationship exists between exercise and survival, whereby beyond an optimal level of fitness, the principle of diminishing returns applies. Indeed, some go further in suggesting that there is evidence that extreme athletic training may be harmful in some individuals. The incidence of sudden cardiac death in athletes is greater than in matched, nonathletic counterparts, and this finding is driven by the provocation of an underlying cardiac abnormality by strenuous exertion. The task of detecting pathological myocardial substrate in athletes is made difficult by physiological adaptations to exercise that can mimic the appearance of cardiomyopathies and ion channelopathies in some individuals. This article details the clinical evaluation of the athlete with reference limits for cardiac physiological remodeling and discusses the diagnostic dilemmas that arise.