The electrophysiological effects of orally administered Amiodarone (600 mg daily for 8 days) were evaluated using His bundle electrograms, the extrastimulus method and atrial pacing in 16 patients with proved ischemic heart disease. Our results show that Amiodarone: 1) does not affect sinus node activity; 2) considerably prolongs the refractory periods of the atrium; 3) slightly and inconsistently prolongs the refractory periods of the atrio-ventricular node and the intraventricular conduction system; 4) slightly decreases the atrio-ventricular conduction; 5) does not consistently depress the intraventricular conduction. These properties contribute to the explanation of the antiarrhythmic effects of the drug.