The third edition of the updated global harmonized definition of myocardial infarction was announced at the ESC Congress held in Munich, Germany, from August 15-29, 2012, and a brief explanation of the main contents and points of the update is presented. The updated definition of myocardial infarction from October 2007 by the European Society of Cardiology (ESC), American College of Cardiology (ACC), American Heart Association (AHA) and World Heart Federation (WHF) defines acute myocardial infarction as the death of myocardial cells due to myocardial ischemia, and this definition remains unchanged in the new edition. The criteria for myocardial infarction defined in the new version are: elevated serum myocardial markers (mainly troponin) (at least above the upper 99% reference value) with at least one of the following clinical indicators: (1) ischemic symptoms; (2) new onset of ischemic ECG changes [new ST-T changes or left bundle branch block (LBBB)]. (3) pathological ECG Q-wave formation; (4) imaging evidence of new loss of myocardial activity or new localized ventricular wall motion abnormalities; and (5) coronary angiography or autopsy confirmed thrombus in the coronary arteries. Article 5 of the new definition is a new addition, the significance of which is to emphasize that once a myocardial infarction has occurred, coronary angiography should be actively performed to verify the cause of the myocardial infarction during the course of medical treatment and to start coronary artery treatment in the early stage. It is also clear from the definitions in the 07 and 12 editions that changes in serum troponin levels are of absolute importance in the diagnosis of myocardial infarction. Elevated serum troponin levels are seen in both type I and type II myocardial infarction, but there is little change in serum troponin levels when there is only myocardial ischemia without necrosis. The new version emphasizes that a diagnosis of myocardial infarction can be confirmed if a patient has typical clinical symptoms of acute myocardial ischemia with an elevated serum troponin level, because an elevated serum troponin level marks the beginning of death of the ischemic myocardium. Analysis of changes in serum myocardial markers (mainly troponin) levels in patients with acute coronary syndromes can be helpful in guiding us on which therapeutic measures to use. 2 Clinical staging of myocardial infarction The new version of clinical staging of myocardial infarction is approximately the same as the 2007 definition. Type 1: spontaneous myocardial infarction due to intracoronary thrombosis caused by coronary plaque rupture, fissure, or entrapment; Type 2: myocardial infarction secondary to an imbalance in myocardial oxygen supply and demand (e.g., coronary spasm, arrhythmia, anemia, respiratory failure, hypertension, or hypotension) leading to ischemia; Type 3: sudden cardiac death suspected to be myocardial ischemia, or suspected to be a new ECG ischemic change or new LBBB of cardiac death. Because death has already occurred, the patient is too late to collect a blood sample for myocardial marker measurements. Type 4 (4a and 4b): myocardial infarction associated with PCI, where type 4 myocardial infarction is divided into type 4a and type 4b; and type 5: myocardial infarction associated with CABG. The difference between type 1 and type 2 myocardial infarction is that the coronary intima in patients with type 1 infarction is unstable, and thrombosis is the main cause of infarction, requiring aggressive treatment such as thrombolysis, antithrombotic and antiplatelet therapy; in type 2 infarction, there is no thrombosis, and dilatation of coronary arteries and improvement of myocardial oxygenation are the main measures of treatment. Type 4 myocardial infarction is associated with PCI and is now classified as type 4a and type 4b. type 4a infarction is defined as myocardial infarction due to the PCI process, including the balloon dilation and stent implantation process, and the criteria are: post-procedure patient with elevated serum troponin levels more than 5 times the upper limit of the 99% reference value and one of the following: symptoms of myocardial ischemia, new ECG ischemic changes, vascularity seen on angiography absence, new loss of myocardial viability, or new imaging evidence of abnormal ventricular wall motion.4 Type 4b infarction was defined as myocardial infarction with stent thrombosis, with criteria such as thrombosis in an ischemia-related vessel on coronary angiography or autopsy and elevation of serum myocardial markers above at least 99% of the upper reference value. Type 5 myocardial infarction is defined as a myocardial infarction associated with CABG in which the patient’s troponin exceeds the upper 99% reference value by a factor of 10 and is associated with one of the following: new pathological Q waves or LBBB on ECG, new intra-bridge (venous or arterial) occlusion confirmed by imaging, new loss of myocardial activity, or new localized ventricular wall motion abnormalities. 3 Diagnostic Definitions and Technical Indicators The technical indicators and criteria for the diagnosis of myocardial infarction in the new version are approximately the same as the 2007 definition. The electrocardiographic criteria and echocardiographic criteria remain unchanged. The following definitions are used: Reinfarction: acute myocardial infarction that occurs again within 28 days after an infarction; Recurrent MI: myocardial infarction that occurs again 28 days after an acute infarction; Silent MI: the patient’s ECG shows pathological Q waves consistent with the diagnosis of infarction or imaging confirms an infarction, but there are no clinical symptoms. However, the following definitions have been added to the new version: infarction associated with surgical operations, such as infarction due to TAVI (percutaneous transluminal valvuloplasty), infarction due to mitral clip, infarction due to radiofrequency treatment of arrhythmias; infarction due to noncardiac surgery; infarction occurring in the ICU; and myocardial ischemia or infarction associated with heart failure. All of these heart attacks bear the name of the causes leading to the occurrence of heart attack, reminding us that heart attack can occur in many cases and that it is important to clarify the causes that trigger heart attack when diagnosing and managing heart attack in order to achieve proper treatment.