In a double-blind randomized clinical trial, 60 elective CABG patients with EF < 50% will evaluated. The patients will numbered according to their reference to the Heart Center of Mazandaran (Iran) and their arrangements in the operation list. They will be randomly allocated to 2 groups of 30 by a computer program to receive either GIK (group G) or NAC (group N).). In group G, 10 cc/h of GIK solution will infuse constantly during the surgery. Group N will injected with a cardioplegic solution containing 200 mg NAC. Normal saline will used as placebo in both groups (injected in group G and infused constantly in group N) to prevent the surgical team form identifying the drugs. A cardiopulmonary bypass pump will used for all cases in both groups.subjects will excluded in case of requiring intra-aortic balloon pump during the operation, prolonged cross-clamp period of 1.5 hours or more, and sensitivity to NAC. EF, Frequency of arrhythmia, need for inotropic drugs during and after the operation, need for shock and pacemaker, commencement of normal heart rhythm, postoperative levels of cardiac enzymes, ECG changes, central venous pressure (CVP), and duration of hospital and intensive care unit (ICU) stay wil bel also recorded and compared between the 2 groups.