Abstract: Heart rhythm disturbances in normal rabbits induced by intravenous (ⅳ 45 mg/kg) or intracerebroventricular(i c v 3 mg/kg) administration of pyquiton were quite similar in frequency(76.5% or 78.9%, respectively) and in ECG (ventricular premature beats or ventricular tachycardia). Injection of phenytoin sodium(3 mg/kg) into the vertebral artery immediately abolished the arrhythmia induced by iv pyquiton. Destruction of the adrenal medulla, reserpinization or icy propranolol significantly decreased the frequency of the arrhythmia induced by icv Pyquiton. Ⅰ cv propranolol or practolol significantly decreased the frequency of the arrhythmia induced by iv pyquiton, but administration of clonidineinto the vertebral artery did not. Our results seem to suggest that pyquiton-induced heart rhythm disturbances in normal rabbits possibly originated from the stimulation of certain central β-adrenergic areas which caused overactivity of the peripheral sympathetic system.