Background: Some evidences have shown the role of antioxidant vitamins in preventing atrial fibrillation (AF) after coronary artery bypass grafting (CABG) surgery. We sought to determine the effect of oral vitamin C on the incidence of postoperative AF in patients undergoing elective isolated on-pump CABG surgery.

Methods: One-hundred patients who underwent isolated CABG surgery were prospectively assigned into two groups: Group 1 — 50 patients received 2 g of oral vitamin C before and 500 mg twice daily lasting for 5 days after surgery; Group 2 — 50 patients as the control group did not receive any. All patients were continuously monitored after surgery in the intensive careunit (ICU), and then Holter monitoring was implemented for 72 h.

Results: The mean of patients’ age was 61.31 ± 6.42 years. Postoperative AF occurred in 16 and 4 patients in control and treatment groups, respectively (32% vs. 8%, p = 0.003). The ICU stay was 1.79 ± 0.313 and 2.10 ± 0.61 days for vitamin C and control groups, respectively (p = 0.002). The hospital stay was significantly lower in vitamin C group compared with that of the control group (5.32 ± 0.59 vs. 5.74 ± 1.30 days, respectively, p = 0.041). Baseline erythrocyte sedimentation rate (OR 1.030, 95% CI 1.003–1.058, p = 0.030) and taking vitamin C (OR 8.068, 95% CI 1.783–36.517, p = 0.007) were the independent predictors of postoperative AF.

Conclusions: Oral vitamin C can be safely used to decrease the incidence of postoperative AF in patients undergoing elective isolated on-pump CABG surgery.