The aim of this study was to compare the efficacy of pulsed versus continuous RF energy delivery via multipolar ablation catheters. In vitro tests were performed in endomyocardial preparations of fresh bovine hearts in a both of physiological saline solution (37 degrees C) at constant flow conditions (1.5 L/min). The catheters were applied to the endocardium at a constant pressure. Energy was delivered pulsed (to 4 electrodes simultaneously, 5-ms duty cycle) or continuously (to each electrode separately). In vivo experiments were performed under fluoroscopy in eight anesthetized pigs, guided by endocardial electrograms to place the catheters in 22 different intraatrial positions. Lesion volume was calculated from measurements of the lesion diameter with a microcaliper. The homogeneity of the lesions was classified from 1 (highest) to 4 (least). More homogeneous linear lesions were produced in significantly less time with pulsed than with continuous energy delivery. There were no differences in electrode temperature or impedance values in vitro and in vivo. The results in the in vitro experiments were reproducible in the intact animal experiments. Significantly larger and more homogeneous linear lesions were created more rapidly with pulsed than with continuous energy delivery.