1. Arrhythmia. It is both one of the main manifestations of acute myocardial infarction and one of the most important comorbidities, seen in 75% to 95% of patients, and is most common within 24 hours of onset. Among all kinds of arrhythmias, ventricular arrhythmias are the most frequent, especially ventricular premature beats. If ventricular premature beats are frequent (more than 5 beats per minute), occur in pairs or more than 2 in a row, with different morphology of multi-source premature beats, or often during the vulnerable period of the previous premature beat (R on the T wave), they are often the precursors of ventricular fibrillation and should be paid great attention. 2. Pump failure. Acute myocardial infarction caused by the heart pumping function is called pump failure, clinical manifestations of left heart failure and cardiogenic shock, the incidence of 32% to 48% and 15% to 20%; severe cases of both conditions can occur at the same time, pump failure patients with acute myocardial infarction area often exceeds 40% of the total area of the left ventricle, mostly occurs in extensive anterior wall infarction. 3. Heart rupture. It is a fatal complication of acute myocardial infarction. The incidence is about 4% to 23%, mostly within one week after infarction, and it occurs more often in elderly people and people with hypertension. Most cardiac ruptures are free wall ruptures, resulting in sudden death due to acute pericardial tamponade caused by blood accumulation in the pericardium. Occasionally, ventricular septal rupture causes perforation, resulting in heart failure and shock and death within a few days. Cardiac rupture can also be subacute, and the patient can survive for several months. 4. Embolism. Its incidence is about 1% to 6%, seen in l to 2 weeks after the onset of the disease, there are two common thrombi: one is in the left ventricular myocardial necrosis, called wall thrombus, this thrombus is dislodged into the circulation, which can cause embolism of the brain, spleen, kidney or extremities and other arteries. Another easy to form thrombus site for the lower extremity veins, and absolute bed rest, cardiac decompensation, once dislodged, with the venous blood flow to the lungs, can cause pulmonary embolism, and in serious cases can cause sudden death. 5.Ventricular expansion tumor. Also known as ventricular wall tumor, the word “tumor” here does not mean a tumor, but a piece of outward bulging, mainly in the left ventricle, the incidence of 5% to 20%. The formation is due to the scar formed after myocardial necrosis, and the scar tissue is weak and easily bulges out under intracardiac pressure, forming a ventricular wall tumor. The tumor is prone to thrombus formation and organ embolism after dislodgement. Ventricular wall tumor can be surgically removed. 6. Post-myocardial infarction syndrome. The incidence is about 10%, which occurs within weeks to months after myocardial infarction, and can recur, manifesting as pericarditis, pneumonia or pleurisy, with fever, chest pain and other symptoms, which may be caused by the body’s allergic reaction to the necrotic material. 7.Shoulder-hand syndrome. The main manifestation is left shoulder and arm straightening, restricted movement and pain may be caused by shoulder and arm inactivity after myocardial infarction, which occurs a few weeks after the onset of the disease and can last for several days to weeks, this syndrome is not rare. Complications are a major cause of death in acute myocardial infarction and should be actively prevented.