Objective To evaluate the efficacy of preoperative infusion of glutamine for myocardial protection in patients undergoing cardiac surgery with cardiopulmonary bypass(CPB). Methods Forty patients, aged 18-80 yr, of ASA physical status Ⅰ-Ⅲ(NYHA Ⅰ-Ⅲ), scheduled for elective cardiac valve replacement and/or coronary artery bypass grafting with CPB, with their left ventricular ejection fraction ≥40%, were enrolled in the study.The patients were randomly divided into 2 groups using a random number table: glutamine group(group G, n=18)and control group(group C, n=22). In group G, the mixture of glutamine 0.4 g/kg(2 ml/kg)and 8.5% compound amino acid(10 ml/kg)was infused over 1 h starting from 24 and 1 h before surgery.Lactated Ringer's solution 12 ml/kg was infused intravenously over 1 h starting from 24 and 1 h before surgery.Before skin incision, at the end of surgery and at 20 h after surgery, venous blood samples were collected for detection of malondialdehyde(MDA)concentrations using ELISA.Before skin incision and at 6 and 20 h after restoration of spontaneous heart beat, venous blood samples were collected to determine the plasma concentration of cardiac troponin I(cTnI). The restoration of spontaneous heart beat, ventricular pacing, postoperative ventilation time, duration of ICU stay, consumption of dopamine and dobutamine during ICU stay, total postoperative length of hospital stay, adverse events such as heart failure, respiratory failure, abnormal hepatic and renal function, and the mortality rate during hospital stay were recorded. Results A total of 15 patients in group G and 18 patients in group C completed the study.Compared to group C, the plasma cTnI concentration at 20 h after restoration of spontaneous heart beat, plasma MDA concentration before operation, at the end of operation and at 20 h after operation, and consumption of dopamine during ICU stay were significantly decreased in group G. There was no significant difference between the two groups in the constituent ratio of mode of spontaneous heart beats, rate of ventricular pacing after spontaneous heart beats, postoperative duration of mechanical ventilation, consumption of dobutamine during ICU stay, duration of ICU stay, postoperative length of hospital stay, incidence of postoperative adverse effects, and mortality rate. Conclusion Although preoperative infusion of glutamine can inhibit oxidative stress response and attenuate postoperative myocardial injury, it provides no clinical significance in the patients undergoing cardiac surgery with CPB. Key words: Glutamine; Cardiac surgical procedures; Cardiopulmonary bypass; Myocardium; Prognosis