The annual incidence of sudden cardiac death in the United States has recently been estimated at 450,000. Most of these patients die from ventricular tachyarrhythmias. Currently, there is a limited ability to predict reliably which patients are at risk for these events. Implantable cardioverter defibrillators (ICDs) are highly effective at treating the arrhythmias that cause sudden death. Multiple clinical trials demonstrating the efficacy of ICDs for the primary prevention of sudden death have been completed, leading to a relaxation of the selection criteria for their use, and therefore a potentially large expansion in the pool of patients eligible for these devices. This has major economic implications for the health care system, and has led to a need for better prospective identification of patients who are or are not at high risk for sudden death.