It is well recognized that poor perioperative blood glucose (BG) control can increase the risk of infection, cardiovascular accidents, and even death in patients undergoing cardiac surgery. Since it has been reported that tight BG control (80-110 mg/dL) yields better outcomes in critically ill patients, it became a standard of care to control BG using intravenous insulin infusion in ICU. However, it has been debated in terms of the optimal target range whether a strict control with intensive insulin therapy is better than liberal control. Because strict BG control can often cause hypoglycemia, which in turn increases the hospital mortality. In fact, a meta-analysis of randomized clinical trials concluded that tight BG control was not associated with significantly reduced hospital mortality but was associated with an increased risk of hypoglycemia. According to the current published guidelines, it seems to be optimal to control BG level of 140-180 mg/dL in ICU. In terms of more strict BG control (110-140 mg/dL), it may be appropriate in selected patients as long as this can be achieved without significant hypoglycemia.