The extra-cardiac sites of action of strophanthin-K, quinidine and procaine amide have been investigated by injection of varying doses into the third ventricle of unanesthetized dogs. A profuse autonomic nervous system discharge was produced. Strophanthin-K produced a paroxysmal ventricular tachycardia resulting in death by ventricular fibrillation. Such effects could be blocked by prior intraventricular injection of either quinidine or procaine amide or by intravenous administration of hexamethonium.