Creatine kinase isoenzyme (CK-MB) is one of the isoenzymes of creatine kinase (CK), most of which comes from the myocardium. It is a very important myocardial index and is of great significance in clinical diagnosis. In the presence of myocardial infarction, the level of CK-MB in human serum is rapidly increased, and it is considered that the activity of CK-MB in the diagnosis of myocardial infarction is more reliable than electrocardiogram. In myocardial infarction, CK-MB increased within 6 hours of onset, peaked at 24 hours, and returned to normal within 3-4 days. The combination of CK-MB and myoglobin and troponin I is a commonly used diagnostic indicator for myocardial infarction.