There remains a significant paucity of information evaluating the effect of glycated HbA1c levels and its theorized effect on mortality and morbidity rates following cardiac surgery. Diabetes is a very common comorbidity in patients undergoing open heart surgery as there is shift in patient characteristics and being higher risk. Currently, the evidences are controversial and there is no clear consensus that increased HbA1c levels is associated with an increased perioperative mortality rate. However, reported literature are more commonly able to demonstrate elevated HbA1c levels to be associated with increased rates of wound infection, cardiovascular events and renal failure; thus, higher morbidities postoperatively. This literature review aims to examine the evidence synthesis behind each of morbidities and mortalities associated with open heart surgery and the impact of high HbA1c on the reported outcomes.