Objective To compare the myocardial protective effects of isoflurane versus sevoflurane in patients undergoing off-pump coronary artery bypass grafting (OPCABG). Methods Forty ASA Ⅱ or Ⅲ patients (NYHA Ⅱ or Ⅲ ) of both sexes, aged 40-55 yr, weighing 55-94 kg, scheduled for elective OPCABG, were randomly divided into 2 groups ( n = 20 each): isoflurane group ( group Ⅰ) and sevoflurane group ( group S). Anesthesia was induced with midazolam, sufentanil and vecuronium. Patients were tracheal intubated and mechanically ventilated. Anesthesia was maintained with inhalation of isoflurane or sevoflurane and infusion of sufentanil and vecuronium. In group Ⅰ, the initial end-tidal concentration of isoflurane was 1.2%. In group S, the initial end-tidal concentration of sevoflurane was 1.7 %. BIS value was maintained at 40-50 by adjusting the end-tidal concentration of isoflurane or sevoflurane. The central venous blood samples were collected immediately before skin incision, at the end of surgery, 2 and 24 h after surgery for determination of plasma creatine kinase-MB (CK-MB) activity and cardiac troponin Ⅰ (cTnI) concentration. The adverse cardiovascular events were recorded. Results The incidences of ventricular premature beat, tachycardia, bradycardia, ventricular fibrillation and S-T segment elevation ( ＞0.1 mV) during surgery and the plasma CK-MB activity and cTnI concentration after surgery were significantly higher in group S than in group Ⅰ ( P ＜ 0.05). Conclusion Isoflurane has better myocardial protective effect than sevoflurane in patients undergoing OPCABG.