Between 1977 and 1986, 589 patients (age, 57 +/- 13 years; 464 men and 125 women) received amiodarone for ventricular fibrillation (VF; 147 patients), sustained (VT-S; 242 patients) or nonsustained (VT-NS; 80 patients) ventricular tachycardia, or supraventricular tachycardia (SVT; 120 patients). Mean left ventricular ejection fraction was 36 +/- 17%, with 23% in New York Heart Association functional class I, 49% in class II, 25% in class III, and 3% in class IV. Sixty-two percent had ischemic heart disease. Follow-up was 32 +/- 27 months (mean +/- SD). Life table analysis revealed that patients with VF, VT-S, and VT-NS had a cumulative incidence of sudden death of 9% at 1 year, increasing by about 3% per year. By years 2 and 5, the cumulative incidence of sudden death, VF, or VT-S recurrence was 26% and 38% and the percent of patients still taking amiodarone was 54% and 32%. For patients with SVT at years 2 and 5, the cumulative incidence of sudden death was 1% and 3%, and of sudden death or SVT recurrence the cumulative incidence was 20% and 29%. The percent of patients still taking amiodarone was 67% and 43%. Of 14 clinical variables assessed, New York Heart Association functional class was the best predictor of sudden death and arrhythmic failure and no other variable added independent predictive power. Older age and lower left ventricular ejection fraction were independent predictors of drug failure (sudden death or arrhythmic failure or need to discontinue amiodarone because of side effects). We conclude that despite its side effect profile, amiodarone is an effective and reasonably well-tolerated antiarrhythmic drug.