We compared effects of the antiarrhythmic drug bepridil on the electrophysiological parameters in the isolated pulmonary vein preparation from guinea pigs with those in the left atrium. Three pairs of bipolar electrodes were attached to the left atrium, pulmonary vein and junctional region of left atrium and pulmonary vein to measure intra-atrial and intra-pulmonary vein conduction velocity and effective refractory period. Bepridil at 10 µM prolonged the effective refractory period with little effect on the conduction velocity in the pulmonary vein, whereas the drug failed to affect the electrophysiological parameters in the left atrium. Using the conventional microelectrode technique, action potential of the isolated pulmonary vein preparation and left atrium were measured. Bepridil prolonged the action potential duration of the pulmonary vein more potently than that of the left atrium. These results suggest that antiarrhythmic effects of bepridil on reentry within the pulmonary vein are estimated to be greater than within the left atrium, which may be one of the key considerations to understand its antiarrhythmic mechanisms.