Life-threatening ventricular arrhythmias in the athlete nearly always occur in the presence of structural heart disease. In the last few years, 2 new causes of life-threatening arrhythmias have been described in patients with normal hearts—that of the Brugada syndrome and that of commotio cordis. Non–life-threatening premature ventricular beats and even nonsustained ventricular tachycardia are not rare, and although usually benign, can be secondary to cardiomyopathies. Athletes with symptoms of syncope, especially if exertional, warrant a complete evaluation. The treatment of athletes and other individuals with life-threatening ventricular arrhythmias has been revolutionized by the implantable cardioverter defibrillator, a device that affords excellent protection from sudden death. Defining those athletes who would benefit from the implantable defibrillator is not always clear. Furthermore, participation in competitive athletics for athletes with life-threatening arrhythmias or structural heart disease known to put the athlete at risk for life-threatening arrhythmias is usually prohibited.