The aim of this study was to investigate the efficacy and the side effects of a long-term treatment with amiodarone. We analyzed the data of 41 patients in whom amiodarone therapy had been initiated between 1974 and 1984. Twenty-one patients had dilative cardiomyopathy, 14 patients had chronic myocardial infarction, four patients suffered from WPW syndrome with intermittent atrial fibrillation, one patient had aortic valve surgery, whereas in one patient there was no clinical evidence of a heart disease. All patients had salvos of ventricular extrasystoles, ventricular tachycardia or documented intermittent ventricular fibrillation. There have been seven drop-outs up to the present time. In each patient, the lowest antiarrhythmically effective dose was applied, which was generally higher in patients with low ejection fraction. Effective treatment of the ventricular tachycardia was achieved in 55-92% of patients and did not depend on the duration of treatment. In 10 patients in whom amiodarone therapy had to be stopped for various reasons. Sudden cardiac death was slightly more frequent than in the 24 patients treated with amiodarone, though the difference was not significant. In cases with a history of syncope the prognosis was poor, even with amiodarone therapy. Due to side effects, a dosage reduction or discontinuation of amiodarone treatment became necessary in 14 patients. Amiodarone proved to be an effective drug also for the long-term treatment of ventricular tachycardia, and possibly for the prevention of sudden cardiac death. With the exception of blue skin color, there was no accumulation of side effects, even during long-term treatment of several years.