Bunaftine is a class III antiarrhythmic agent which has been found effective in treating or preventing both ventricular and supraventricular arrhythmias. The acute electrophysiologic effects of intravenous Bunaphtine 1,5 mg/kg body weight, were studied in 19 subjects with estimated normal impulse formation and conduction. Significant effects were sinus bradycardia, prolongation of atrial refractory periods, depression of intranodal and infranodal conduction and prolongation of His-Purkinje system refractory periods. These properties are compared with those of amiodarone and quinidine and form the basis for correct use of Bunaphtine in the management of arrhythmias