Abstract: AIM:To study the role of 3 days of potassium magnessium aspartate after off-pump coronary artery bypass graft (OPCABG) surgery in preventing postoperative atrial fibrillation (AF). METHODS: One hundred sixty patients undergoing isolated, initial CABG surgery and having sinus rhythm before surgery were alternatively randomized into the study or the control group (n=80). The patients in the study group received 4 g potassium magnesium aspartate in 250 ml of 5% glucose solution infused intravenously for 3 days. Patients in the control group received 250 ml of 5% glucose solution infused intravenously for 3 days. Exclusion criteria included history of AF, implanted pacemaker, postoperative myocardial infarction, pump CABG in operation and renal failure. The end point was development of AF after operation. RESULTS: The incidence of AF was 9% in patients who received 3 days of potassium magnesium aspartate. Patients without potassium magnesium aspartate had an AF incidence of 19% (P<0.01). The ICU stay was also shorter in the treated group (P<0.05). CONCLUSION: A 3-day postoperative infusion of potassium magnesium aspartate is safe and effective in reduction of possible life-threatening AF in patients undergoing off-pump coronary artery bypass graft surgery.