Amiodarone, 600 mg orally daily, was used in an attempt to control supraventricular tachyarrhythmias in a patient with the sick sinus syndrome. Twenty days from the onset of therapy the Q-T interval lengthened. Episodes of ventricular flutter, ventricular fibrillation and self-terminating ventricular tachyarrhythmia (torsade de pointes) developed on the 28th day of amiodarone therapy. Temporary cardiac pacing prevented further episodes of ventricular fibrillation. Despite the suggestion that this drug may be given in large doses for long periods of time since it has a wide safety margin, we feel that the risk of lethal arrhythmias is such that caution is required in its use.