Acute hyperglycemia is a common feature during the early phase after acute myocardial infarction (AMI), regardless of diabetes status. Numerous studies have demonstrated that patients with AMI and hyperglycemia on admission have high rates of mortality. It has been reported that there is a linear positive relation between admission blood glucose levels and mortality after AMI. However, recent studies showed that the relationship is U-shaped in patients with a history of diabetes. Diabetic patients with moderate hyperglycemia (glucose 9-11 mmol/L) had the lowest mortality and not only severe hyperglycemia (glucose ≥ 11 mmol/L) but also euglycemia (glucose < 7 mmol/L) was associated with higher mortality. Although it has been debated whether acute hyperglycemia is causally related to adverse outcomes after AMI or is simply an epiphenomenon of severely damaged myocardium, multiple physiological studies have demonstrated that hyperglycemia has a direct detrimental effect on ischemic myocardium through several mechanisms, including oxidative stress, inflammation, apoptosis, endothelial dysfunction, hypercoagulation, platelet aggregation and impairment of ischemic preconditioning. Current guidelines recommend the use of an insulin-based regimen to achieve and maintain glucose levels < 10.0 mmol/dl, and emphasize the avoidance of hypoglycemia. However, the optimal management goal of glucose levels for patients with acute hyperglycemia remains uncertain. Further studies are warranted into the appropriate management in patients with AMI and acute hyperglycemia.