The most serious symptom of acute myocardial infarction is sudden death, and the causes include shock, arrhythmia and heart failure. 1. Shock: In patients with myocardial infarction, myocardial necrosis is extensive, cardiac output drops sharply, and cardiogenic shock occurs. It also includes peripheral vasodilatation caused by nerve reflexes, and in some patients, there is also the involvement of blood volume insufficiency. 2. Arrhythmia: acute myocardial infarction can cause various arrhythmias, such as ventricular pre-systole, ventricular fibrillation, etc., which can cause sudden death. Ventricular fibrillation is likely to occur in the early stage of ST-segment elevation myocardial infarction, especially the main cause of death before hospitalization. 3. Heart failure: After myocardial infarction, the diastolic force of the heart is significantly weakened or uncoordinated, leading to heart failure and causing sudden death. The typical symptom of acute myocardial infarction is sudden, persistent and severe pressure pain in the retrosternal or precordial area, which cannot be relieved by rest and nitroglycerin. If myocardial infarction is suspected, you should go to the hospital immediately to avoid delaying treatment.