Abstract: AIM:To evaluate the safety and beneficial effect of repeated hyperbaric oxygen (HBO) preconditioning as an adjunctive therapy for myocardium protection in clinical trials of coronary artery bypass graft (CABG) surgery. METHODS: Forty nine patients were prospectively randomized into control group (n=25) and HBO preconditioning group (n=24) before CABG surgery. Control group included 15 patients undergoing on-pump surgery and 10 patients undergoing off-pump surgery. HBO group included 14 patients undergoing on-pump surgery and 10 patients undergoing off-pump surgery. Patients in HBO group were intermittently exposed to hyperbaric oxygen for 120 min at 2.0 ATA, once daily for 5 consecutive days before surgery. Serum troponin I (cTnI) concentration was determined, and blood samples were taken from radial artery pressure line at sevem time points, respectively, before induction of anesthesia, arrival at ICU and 6, 12, 24, 48 and 72 h after surgery. Inotrope score was calculated from the time point of ICU arrival to 48 h after surgery. RESULTS: Patient characteristics were comparable in the two groups. In patients with on-pump surgery, serum cTnI release was lower in HBO group during the time point from ICU arrival to 48 h after surgery (P<0.05). Inotrope score during the period from 24 to 36 h after surgery was lower in the HBO group compared with that in control group (P<0.05). However, serum cTnI concentration and inotrope score were similar in both groups in patients with off-pump surgery. CONCLUSION: A modality of repeated preconditioning with HBO is safe and well tolerated in patients undergoing CABG surgery. HBO preconditioning reduces the release of serum cTnI and inotropic drug use in on-pump CABG surgery but has only a limited protective effect on patients undergoing off-pump surgery.