T HE IMPLANTABLE cardioverter-defibrillator is an effective nonpharmacological method for the termination of ventricular tachycardia or ventricular fibrillation. In patients who have survived a previous cardiac arrest, defibrillator therapy is associated with a low incidence of subsequent sudden death (1% to 2% annually)‘-” and is widely advocated as the treatment of choice in this patient subgroup.8T9 Multiplefunction, tiered therapy devices that provide antitachycardia pacing and low-energy shocks have extended the potential applications of the device to patients with recurrent hemodynamitally stable sustained ventricular tachycardia.‘O The use of nonepicardial lead systems,“.” permitting implantation without thoracotomy, has further enhanced patient and physician acceptance of this therapeutic modality. Despite two decades of specialized emergency prehospital care, survival to hospital discharge following out-of-hospital cardiac arrest remains poor, ranging from 2% to 25% (approximately 10% in most communities); survival is determined in part by the extent and sophistication of emergency systems.13-‘” Use of the automatic external defibrillator significantly improved short-term survival in an initial largescale field study.” Further experience with this device in a variety of community settings will be necessary to determine its overall impact on patient salvage. Several recent trials of pharmacological interventions aimed at reducing the incidence of sudden death in high-risk patients have provided discouraging results.rR-iy These observations, combined with the widespread acceptance of defibrillator therapy in patients with prior sustained ventricular arrhythmias, have led to increased interest in the use of the implantable defibrillator as prophylactic therapy in high-risk patients before the first episode of a potentially fatal ventricular tachyarrhythmia. The vast majority of unexpected cardiac arrests and sudden deaths (up to 90%) occur in patients with coronary artery disease.‘OJ A substantial proportion of such deaths occur in patients with previously identified heart disease and evidence of prior myocardial infarction.“-‘4 This latter population thus provides a logical starting point for prophylactic interventions, including the implantable defibrillator. The purpose of this review is to examine the potential role of prophylactic implantable defibrillators in enhancing survival rates in high-risk patients following myocardial infarction. Several factors must be considered in evaluating the feasibility and efficacy of such an approach. First, potential survival benefit is linked to the complex pathophysiology of death following myocardial infarction, including competing risks of death due to arrhythmias, pump failure, and acute myocardial ischemia (and the possibility that the device may merely alter the mode of death). In addition, postinfarction survivors are not a homogeneous group with respect to risk of