The Antiarrhythmics Versus Implantable Defibrillators (AVID) study compares a strategy of initial treatment with an implantable cardioverter-defibrillator (ICD) to a strategy of initial treatment with an antiarrhythmic drug to prevent death in patients with a history of ventricular fibrillation or hemodynamically compromising ventricular tachycardia, or both. Neither arrhythmia can have been due to a transient or correctable cause. The principle exclusions are a contraindication to amiodarone therapy and inability to undergo ICD implantation. Antiarrhythmic drug therapy includes empiric amiodarone and guided sotalol. The ICDs allowed are advanced generation devices, and most are implanted transvenously. The primary end point of the study is total mortality. Secondary end points are cost and quality of life. The study was designed in 2 phases. The pilot phase enrolled 200 patients between June 1993 and June 1994. Data collected during the pilot phase confirmed that the trial is feasible. An additional 1,000 patients will be enrolled between June 1994 and March 1997. It is anticipated that all 1,200 patients will be followed until September 1998, and will be included in the intention-to-treat analysis.