Implantable cardioverter-defibrillators (ICDs) are one of the few interventions where we can be reasonably confident that a patient did or did not benefit from the treatment. If one is to benefit from an ICD, then the person must survive long enough to have an arrhythmic event and receive therapy from the device. Thus, the patients who benefit the most are those with a high rate of arrhythmic death and a low rate of nonarrhythmic death. Indeed the enrollment criteria for clinical trials of ICDs were designed to optimize these 2 rates. Accordingly, the patients enrolled in the primary prevention ICD trials were much younger and had less comorbidity than the community heart failure population.¹