Efficacy, side effects and predictors of response for intravenous amiodarone were evaluated in 46 patients with recurrent drug-refractory sustained ventricular tachycardia or ventricular fibrillation, or both, who were treated with intravenous amiodarone. Of the 46 patients, 27 (58.5%) responded early to intravenous amiodarone and 6 (13%) showed a late response to amiodarone. The majority of patients who responded to intravenous amiodarone did so within the first 2 h of therapy, and all responded within 84 h. Patients with an ejection fraction greater than 25% were more likely to respond (p less than 0.05). Major side effects occurred in 13% of patients. The cumulative 2 year mortality rate due to arrhythmia recurrence or sudden death for responders discharged from the hospital was 23% and the cumulative overall 2 year mortality rate was 46%. In conclusion, intravenous amiodarone is rapidly effective in the majority of patients with recurrent ventricular tachycardia or ventricular fibrillation refractory to other drugs. The poor long-term outcome of patients who require this therapy, respond to it and are discharged on long-term oral amiodarone therapy warrants consideration of other long-term treatment of these patients. Use of intravenous amiodarone is an important new modality in the treatment of drug-refractory malignant ventricular arrhythmias.