Background: During CABG cardioplefic solution is used for cardiac arrest and myocardial protection but there is no defined safety interval time for cardioplegia infusion. Measuremen of the metabolite release from myocardial cells in coronary sinus implicateis accurate protective effect and safety interval of cardioplegia Materials and Methods: Thirteen patients that were scaduled for CABG cold blood cardioplegia transfused via aortic root. Coronary sinus blood samples were taken before and after cross clamping of the aorta at the times of 7, 14 and 20 minutes. The samples were analyzed for pH and lactate immediately. Results: The pH and lactate concentration in coronary at the time of 15 minute after the second dose of transfusion of blood cardioplegia were out of the range of acceptable level (pH=7.22±0.047 lactate=21±2.859mg/dl ρ=0.02). Conclusion: This study indicates that safe interval time between the first and second dose of cardioplegia transfusion was 20 minute and the between second and third dose was 15 minutes.