Mortality is an end point that is unequivocal, for dead is dead (7). Categorization of the mechanism of cardiac death, especially when death occurs out-of-hospital, is imprecise for it is based on retrospective clinical data involving the circumstances and the location of death, pre-morbid clinical symptomatology that is often difficult to ascertain after the fatal event, and the time course of the terminal event. The error rate associated with the subclassification of cardiac death into sudden and non-SCD may be quite large, whether autopsy findings are available or not. Analyses by the Multicenter Automatic Defibrillator Implantation Trial (MADIT-II) End-point Review Committee using the Hinkle-Thaler mortality classification system (8) are shedding some light on this topic (H. Greenberg, personal communication, 2003). Sudden cardiac death accounted for 62% of the cardiac deaths in the conventionally treated MADIT-II patients, and 35% in the ICD group. The reduction in mortality with the ICD was almost exclusively the result of a decrease in cardiac death categorized as SCD. Using various assumptions about the efficacy of the ICD in preventing sudden death in MADIT-II, it appears that the imprecision, that is, the misclassification rate, in categorizing death as sudden due to suspected ventricular tachycardia/fibrillation may be an overclassification in the range of 20% to 30%.