New technologic development of implantable cardioverter-defibrillators (ICDs) keeps up with the exponential increase of their use for primary and secondary prevention of sudden cardiac death. The first-generation ICD with limited shock capability alone could be considered adequate in most cardiac arrest victims, but it was not suitable for sudden death prevention in all high-risk patients with cardiac disease. The second-generation ICD was comprised of hybrid pacemaker-defibrillator systems that provided on-demand ventricular antibradycardia pacing. The third-generation devices include additional functions, such as antitachycardia pacing for ventricular tachycardia (VT) reversion and low-energy ventricular cardioversion, in addition to ventricular defibrillation and single-chamber ventricular demand pacing. In the near future, advanced dual-chamber atrioventricular (AV) pacing and defibrillating systems will also be available. The dual chamber ICD will allow atrial inhibited/dual-chamber (AAI/DDD) rate-responsive pacing, simultaneous atrial and ventricular sensing to optimize the arrhythmia identification, and ICD shock delivery in the proper arrhythmia-related chamber. Clinical benefits of these devices compared with their cost and complexity will require careful evaluation. (Am J Cardiol 1996;78(suppl 5A):116–118)