Approximately 20-25% of patients with myocardial ischemia are asymptomatic. Painless myocardial ischemia, also called asymptomatic coronary artery disease or occult myocardial ischemia (SMI), is a pathological state in which the blood perfusion to the heart is reduced, resulting in reduced oxygen supply to the heart and abnormal myocardial energy metabolism, which cannot support the normal work of the heart, but the patient has no chest pain or subjective symptoms related to myocardial ischemia at the onset and does have objective evidence of myocardial ischemia (abnormalities in electrical activity, left ventricular function, myocardial blood flow The patient does have objective evidence of myocardial ischemia (abnormalities in electrical activity, left ventricular function, myocardial blood flow and perfusion, and myocardial metabolism). These patients are often missed because of atypical symptoms, and coronary angiography or postmortem examination almost always confirms significant stenotic lesions in major branches of the coronary arteries. Asymptomatic myocardial ischemia is very common in coronary artery disease, and the consequences are sometimes severe. Acute myocardial infarction can occur suddenly, or it can slowly progress to heart failure, and some patients can die suddenly and suddenly. Myocardial ischemia can cause reversible or permanent damage to the myocardium and lead to angina pectoris, arrhythmia, pump failure, acute myocardial infarction or sudden death, therefore, it has attracted increasing attention as an independent type of coronary heart disease.