Glutamine is the most abundant free amino acid in the body. It modulates immune cell function and is an important energy substrate for cells in critically ill patients. Reduction of injury cardiac markers had been observed in patients receiving intravenous glutamine and in a pilot study with oral glutamine. The aim of this study was to analyze the effect of preoperative oral supplementation of glutamine on postoperative serum levels of cardiac injury markers. A randomized clinical trial was performed in 28 Mexican patients with ischemic heart disease who underwent cardiopulmonary bypass with extracorporeal circulation. Patients were randomly assigned to receive oral glutamine (0.5 g/kg/day) or maltodextrin 3 days before surgery. Cardiac injury markers as troponin-I, creatine phosphokinase, and creatine phosphokinase-Mb were measured at 1, 12, and 24 hours postoperatively. At 12 and 24 hours serum markers levels were significantly lower in the glutamine group compared with controls (p = 0.01 and p = 0.001, respectively) (p = 0.004 and p < 0.001, respectively). Overall, complications were significantly lower in the glutamine group (p = 0.01, RR = 0.54, 95% CI 0.31-0.93). Mortality was observed with 2 cases of multiple organ failure in control group and 1 case of pulmonary embolism in glutamine group (p = 0.50). Preoperative oral glutamine standardized at a dose of 0.5 g/kg/day in our study group showed a significant reduction in postoperative myocardial damage. Lower cardiac injury markers levels, morbidity and mortality were observed in patients receiving glutamine.