Sudden cardiac arrest claims 350,000 to 450,000 lives per year in the United States alone and is responsible for more than half of all deaths that are due to cardiovascular disease. Our ability to recognize patients who are at high risk for cardiac arrest has improved, but 90 percent of cases of sudden death from cardiac causes occur in patients without identified risk factors. Although the majority of cases of sudden death from cardiac causes involve patients with preexisting coronary heart disease, cardiac arrest is the first manifestation of this underlying problem in 50 percent of patients. The sudden death . . .