Antiarrhythmic drug therapy in patients with implantable cardioverter defibrillators (ICDs) has decreased over the last 10 years. This trend, primarily seen with class I agents, has occurred mainly in patients with a cardiac arrest. However, despite this overall decrease, antiarrhythmic drug therapy remains an important adjuvant to ICD therapy. In addition to primary prevention of ventricular tachycardia and supraventricular tachycardia, antiarrhythmic drug therapy may potentiate tachycardia rate slowing and make ventricular tachycardia more tolerated hemodynamically and possibly more amendable to pacing therapy. Some of the class III antiarrhythmic drugs may actually lower defibrillation threshold. Unfortunately, these drugs may have adverse interactions with ICDs. An increase in defibrillation threshold or rate-dependent increase in pacing threshold may interfere with the effectiveness of device therapy. Proarrhythmic effects of antiarrhythmic drugs may enhance the frequency of device use. The bradycardic effects of antiarrhythmic drug therapy may similarly enhance the requirements for persistent bradycardia pacing and lead to early battery depletion and other adverse consequences. An awareness of potential benefits and adverse effects of antiarrhythmic drug therapy along with careful electrophysiologic assessment are necessary for optimum combination drug and device therapy.