The electrophysiological effects of intravenous bepridil were studied at doses of 2 mg/kg and 3 mg/kg. The drug was tested on 25 patients of both sexes who were undergoing electrophysiological investigation for other reasons (11 normal ECGs, 11 pathological ECGs, 3 WPW syndromes). Electrophysiological parameters before and after bepridil were compared. The following changes were noted: - the refractory period was significantly prolonged at all conducting levels; - the sinus cycle was significantly lengthened in a practically constant fashion (+9,2 p. 100); - conduction in the sinoatrial and atrioventricular nodes was significantly prolonged (+15 p. 100 and + 11 p. 100); - the Luciani-Wenckebach point was significantly decreased in the anterograde, and even more so in the retrograde, directions (-20 and -23 p. 100 respectively); - however, infrahisian conduction was not affected either in patients with normal or pathological ECGs. The drug was effective in blocking the accessory pathway in two of the three patients with the WPW syndrome. A study of drug plasma levels did not show a dose-effect relationship. The plasma levels were extremely variable from one subject to another, suggesting tissue fixation of the active part of the molecule. These results demonstrate the valuable electrophysiological effects of bepridil which, by its mode of action, is very similar to amiodarone.