Bethanidine sulfate is a chemical and pharmacologie analog of bretylium tosylate that has virtually identical antifibrillatory and inotropic actions on the heart. Bretylium is the only drug approved by the Food and Drug Administration specifically for the "prophylaxis and treatment of ventricular fibrillation." Unlike bretylium, which is poorly absorbed from the gut and limited to parenteral use, oral bethanidine is absorbed rapidly. Bethanidine was given to 23 patients with recurrent multiple drug refractory ventricular tachycardia and fibrillation. Eighteen patients (78%) had complete suppression of spontaneous or electrophysiologically inducible tachyarrhythmias; 3 were improved and 2 had no benefit. In 6 of a 9 patient subgroup studied by programmed electrophysiologic drug testing, bethanidine completely prevented previously inducible ventricular tachyarrhythmias at the maximal stimulus tested (including 4 extrastimuli and burst-pacing at 10 times threshold). Cardiac output measured in 6 patients 1 to 2 hours after bethanidine was increased in 4, unchanged in 2, and decreased in 1. Ten patients on long-term therapy with bethanidine and protriptylene (to prevent orthostatic hypotension) have been free of arrhythmias from 2 to 26 (average 13) months.