Background. The effects of exogenous L-aspartate and L-glutamate-enriched cardioplegia on postoperative left ventricular functions after coronary artery bypass surgery in patients with moderate left ventricular dysfunction (left ventricular ejection fraction [LVEF] = 30-40 %) were studied. Methods: In this prospective randomized study, 22 patients with moderate left ventricular dysfunction (mean LVEF = 37.27 % +/- 3.43 %), who underwent elective coronary artery bypass surgery, were examined. Isothermic substrate-enriched [L-aspartate and L-glutamate (13 mmol/L)] blood cardioplegia was used in 11 patients (Group AG), and cardioplegia including only potassium and sodium bicarbonate was used in 11 patients (Group C). All hemodynamic parameters for left and right heart were studied in both groups. Total perfusion time was 126.63 +/- 44.91 minutes versus 114.81 +/- 43.66 minutes (p = 0.54). The aortic cross-clamp time was 77.09 +/- 28.02 minutes versus 67.81 +/- 22.77 minutes (p = 0.4), respectively. The amount of cardioplegic solutions were 7218.2 +/- 3043.6 mL versus 5454.5 +/- 3048.1 mL (p = 0.167). Mean number of distal anastomosis were 3 +/- 0.89 versus 2.9 +/- 0.7 (p = 0.793). Results: There was no difference between both groups in intra-and postoperative periods. In coronary sinus blood gas measures, myocardial acidosis caused by the aortic cross-clamp was found to be more severe in the Group C, but delta pH (0.12 +/- 0.14 vs. 0.092 +/- 0.058; p = 0.613) and delta lactate (1.39 +/- 1.03 vs. 1.62 +/- 0.85; p = 0.579) were similar in both groups. Free oxygen radical production caused by aortic cross-clamp was significant in the Group C. Not all myocardial enzymes, but Troponin-T levels were found higher in control group than the study group (0.6 +/- 0.36 vs. 0.36 +/- 0.25; p = 0.1). Conclusions: Although L-aspartate and L-glutamate favor myocardial metabolic functions, they do not have any affect on myocardial functional recovery in patients with moderate left ventricular dysfunction.