Constantly coupled bigeminal rhythm of long duration induced by infusion of epinephrine into cyclopropane-anesthetized dogs may be converted to multifocal ventricular tachycardia by increasing the blood pressure without changing the infusion rate. Multifoeal arrhythmia may be converted to bigerniny or to sinus rhythm by decreasing the blood pressure but is not converted to ventricular fibrillation by an increase in systemic pressure. Stimulation of the peripheral end of either vagus can convert bigerniny to normal rhythm or increase the coupling interval. Multifocal ventricular tachycardia is converted to sinus rhythm or to bigeminy by stimulation of the vagus. The vagal effect, which is blocked uniformly by atropine, also may be demonstrated when the atrial rate is maintained constant. Vagal stimulation does not increase the threshold dose of epinephrine necessary for induction of ventricular fibrillation. It is concluded that multifocal ventricular tachycardia is due to a mechanism similar to that causing bigeminy, which was shown previously not to be due to the emergence of a focus of increased ventricular automaticity. Both of these arrhythmias probably originate in the bundle of His and differ fundamentally from ventricular fibrillation.