The prevalence of diabetes mellitus among patients undergoing cardiac surgery is rising. These patients have higher perioperative morbidity and mortality. Achieving optimal glycemic control in the perioperative period is critical. Hyperglycemia can impair immune function, making patients more susceptible to infections and can affect the body’s ability to recover following surgery. Diabetic patients are at higher risk for adverse cardiovascular events, following cardiac surgery. Maintaining glycemic control can lower the risk of short-term mortality and long-term survival rates after cardiac surgery. Glycemic control is achieved by implementing various strategies, which include: preoperative optimization, adjusting diabetic medications prior to surgery, intraoperative monitoring blood glucose levels closely, and using insulin or other medications as necessary during surgery. Postoperatively continuing to monitor and manage blood glucose levels in the recovery phase. Anesthesia can disrupt normal glucose metabolism, impairing the body’s ability to regulate blood sugar levels. Hyperglycemia adversely affects the immune system. Increased blood glucose levels can lead to reduced chemotaxis and phagocytosis, which are essential for the immune response to infections. The presence of hyperglycemia can lead to the upregulation of pro-inflammatory cytokines and increased expression of adhesion molecules, which may result in enhanced vascular permeability and immune cell recruitment to sites of injury or infection. Hyperglycemia negatively influences the complement system, which plays a crucial role in immune defense. Impaired complement function can reduce the body’s ability to clear pathogens. Additionally, nitric oxide, which is important for vascular function and immune response, may be produced in suboptimal amounts in hyperglycemic states. The cumulative effects of impaired immune function and increased inflammation can lead to multi-organ dysfunction. Insulin therapy is commonly used to manage hyperglycemia, but the method of delivery and timing can vary, leading to a lack of consensus. As ongoing research continues, advancements in technology (such as continuous glucose monitoring) and personalized medicine could contribute to improving perioperative glycemic management in cardiac surgery. Despite the emerging recognition of the importance of glycemic control, there are no specific guidelines as to what the optimal level of glucose should be during the perioperative period. Future studies regarding the important issues in the management of hyperglycemia during cardiac surgery remain to be elucidated.