Between October 1999 and December 2000, 52 patients (37 male) undergoing coronary artery bypass surgery were selected for overdrive biatrial pacing to determine its effectiveness in reducing atrial fibrillation. A pacing wire was attached to the right atrial appendage and another to the roof of the left atrium behind the aorta. The atria were paced continuously in AAI mode at a rate of 90 pulses per minute or 10 pulses above the underlying rate (maximum rate < 140/min) for 3 days. The endpoint was the onset of atrial fibrillation during hospital stay. Results were compared with those of a control group of 52 matched patients. There were no significant differences in the occurrence of atrial fibrillation (30% in the paced group vs. 25% in the control group), morbidity, or length of hospital stay. Continuous biatrial pacing after coronary bypass surgery was safe and well tolerated, however, it did not prevent or lower the incidence of atrial fibrillation.