Randomized controlled trials have shown superior survival rates with implantable cardioverter defibrillators (ICDs) compared with antiarrhythmic drugs in survivors of cardiac arrest and life-threatening ventricular tachyarrhythmias, as well as in high-risk patients with ischemic heart disease and inducible ventricular tachycardia (VT). Current defibrillators are small and implanted with techniques similar to standard pacemakers. They provide high-energy shocks for ventricular fibrillation (VF) and rapid VT, antitachycardia pacing for monomorphic VT, and antibradycardia pacing. Limited evidence suggests that ICD therapy is cost-effective when compared with other widely accepted treatments. The use of ICDs is likely to continue to expand in the future. Ongoing clinical trials will define further prophylactic indications of the ICD and clarify its cost-effectiveness ratio in different clinical settings.