In general, the chronic phase of myocardial infarction is characterized by T-wave inversion 2-3 months after the onset of acute myocardial infarction. Acute myocardial infarction is a lack of myocardial blood supply due to sudden coronary occlusion, which can cause myocardial necrosis. The staging of myocardial infarction varies according to the severity of the disease. Generally, myocardial infarction within 2 weeks of onset is called the acute phase, 2-4 weeks is called the subacute phase, and after 2-3 months it can enter the chronic phase of myocardial infarction, also known as old myocardial infarction. After the occurrence of myocardial infarction, absolute bed rest is required, oxygen, analgesia and heart load reduction treatment are given, emergency PCI or drug thrombolysis is performed as early as possible within the time window to save the dying myocardium, timely correction of arrhythmia, cardiogenic shock and heart failure, and platelet-lowering and lipid-lowering treatment are given. Untimely treatment of acute myocardial infarction can be life-threatening and must be immediately treated in the cardiology department of the hospital.