Because of a perceived high frequency of ventricular fibrillation when a pacemaker catheter was placed in the right ventricular apex during PTCA, we reviewed our first 400 cases for this complication. The incidence of ventricular fibrillation in the entire group was 10 of 400 cases (2.5%) compared with 17 of 3,806 (0.4%) diagnostic coronary arteriograms performed in our laboratory during the same time period (P less than .001). Ventricular fibrillation occurred more frequently during PTCA when the pacemaker catheter tip was placed in the right ventricular apex (8 of 63 cases, 12.6%) than when it was positioned in either the pulmonary artery, vena cava, or when a pacemaker catheter was not used (2 of 337 cases, 0.6%, P less than .001). Based on these data we have developed a policy of inserting temporary pacemakers prophylactically during PTCA only for patients undergoing dilation of dominant right or dominant left circumflex coronary arteries and in patients with acute myocardial infarction.