The automatic implantable cardioverter-defibrillator (AICD) has become widely accepted as an effective treatment for patients with ventricular fibrillation or hemodynamically unstable ventricular tachycardia. The use of an antitachycardia pacemaker in combination with the AICD has also provided an effective therapy for patients with hemodynamically stable ventricular tachycardia that is refractory to antiarrhythmic drugs. The risk of sudden cardiac death following implantation of an AICD in patients with malignant ventricular tachyarrhythmias is lower than has been observed during treatment with amiodarone, direct operations for ventricular tachycardia, or conventional antiarrhythmic drug therapy guided by either noninvasive or invasive electrophysiologic testing. Although the impact of this device on the subsequent risk of sudden death is widely recognized, the effect on overall mortality is more controversial. Careful preoperative evaluation, electrophysiologic testing, and patient selection are critical for the successful use of antitachycardia devices. Clinical trials of AICDs with the capability for antitachycardia and bradycardia pacing, programmable pulse energy and waveform, and extensive memory will soon begin in the United States. Despite considerable limitations in the currently available technology, future developments in implantable antitachycardia devices offer the greatest promise for improving the outcome of patients at risk for sudden cardiac death from ventricular arrhythmias.