Atrial pacing is often necessary during cardiac surgery. A total of 20 patients undergoing cardiac surgery were atrially paced with either a multipurpose pulmonary artery catheter (PAC) or an A-V paceport PAC (n = 10 each). Atrial pacing was successful in all the patients before cardiopulmonary bypass. The output threshold was 4.2 +/- 0.7 mA for a multipurpose PAC and 3.8 +/- 0.7 mA for A-V paceport PAC. Atrial pacing with both PAC's was readily performed and useful during cardiac surgery.