The precursor of heart attack in the middle of the night is that blood clots in the middle of the night lead to ischemia and hypoxia of the heart, triggering the preexisting manifestations of acute myocardial infarction, chest tightness and discomfort, cough and cold hands and feet. 1. Chest tightness and discomfort: when sleeping in the middle of the night, blood flow slows down, easy to form blood clots. The thrombus will free to the heart or lungs, obstructing the blood supply to the heart or lungs and leading to oxygen deprivation, resulting in chest tightness and discomfort. If the heart continues to supply insufficient oxygen, acute myocardial infarction occurs. 2. Cough: lying flat in the middle of the night, blood flow slows down, stagnation in the lungs, may produce blood clots, obstructing the blood supply to the heart muscle leading to hypoxia and lung stagnation, triggering involuntary cough. 3. Cold hands and feet: in the middle of the night, the blood flow rate decreases, the circulation slows down, easy to produce blood clots, not only can cause acute myocardial infarction, at the same time, blood clots can impede the blood flow of the hands and feet, so that the hands and feet are cold. When the above symptoms occur, it is recommended to seek timely medical treatment to avoid serious consequences.