As a physician, coach, or trainer, we see athletes as healthy, physically fit, and able to tolerate extremes of physical endurance. It seems improbable that such athletes may have, on occasion, underlying life-threatening cardiovascular abnormalities. Regular physical activity promulgates cardiovascular fitness and lowers the risk of cardiac disease. However, under intense physical exertion and with a substrate of significant cardiac disease--whether congenital or acquired--athletes may succumb to sudden cardiac death. The deaths of high-profile athletes receive much attention through the national news media, but there are also deaths of other athletes. With repetitive, intense physical exercise, the heart undergoes functional and morphologic changes. Knowledge of those changes may help one identify cardiovascular abnormalities that can cause sudden death from the heart known as an "athlete's heart." This article will review cardiovascular diseases that may limit an athlete's participation in sports and that may put an athlete at risk for sudden cardiac death. It also reviews the extent and limitations of the cardiovascular preparticipation screening examination. Team physicians, coaches, and trainers must understand the process of evaluation of a symptomatic athlete that may indicate significant cardiac abnormalities. Finally, guidelines to determine eligibility of athletes with cardiovascular disease to return to sports will be reviewed.