In general, diabetes mellitus can be treated with cardiac bypass surgery as long as the blood glucose is properly controlled; diabetes mellitus cannot be treated with cardiac bypass surgery because of sudden blood glucose abnormalities or other contraindications to surgery. 1. Diabetes-related contraindications to surgery: poor glycemic control before surgery, persistent glucose increase, diabetic ketoacidosis, hyperosmolar hyperglycemia syndrome, hypoglycemia, etc. 2. Non-diabetes-related surgical contraindications (1) Severe diffuse calcified cardiovascular lesions or poor distal vascular conditions. (2) Presence of cardiac tamponade or acute myocardial infarction. (3) Coagulation disorders. (4) Serious impairment of hepatic or renal function or cardiovascular function. Whether a diabetic patient can undergo cardiac bypass surgery needs to be comprehensively judged by a specialized clinician according to the condition.