Inclusion Criteria:  - Myocardial infarction group: case group  This group includes acute myocardial infarction (ST segment elevation and non ST segment elevation) and old myocardial infarction. The diagnostic basis of acute myocardial infarction: cardiac biomarkers (cardiac troponin and / or myocardial enzymes) increased or decreased, at least once the value exceeded the upper limit of normal, and there was the following evidence of myocardial ischemia: (1) clinical symptoms of myocardial ischemia（ 2) New changes of myocardial ischemia appeared in ECG, i.e. new ST segment changes or left bundle branch block（ 3) Pathological Q wave appeared in ECG（ 4) Imaging evidence showed new loss of myocardial viability or regional wall motion abnormalities. Diagnosis basis of old myocardial infarction: Patients with previous history of myocardial infarction and confirmed by Peking University Third Hospital, first hospital, Asian heart hospital and Taiyuan cardiovascular hospital.  3.4.2 non coronary heart disease group: control group  The patients in the control group can be enrolled if they meet any of the following criteria: (1) if the patients have no typical symptoms of coronary heart disease, and there is no obvious stenosis on coronary angiography and / or coronary CT (the degree of stenosis in the main coronary artery is less than 30%)（ 2) if the patient had no typical symptoms of coronary heart disease, and the risk factors of coronary heart disease (smoking, hypertension, diabetes, hyperlipidemia, family history of premature coronary heart disease) were not more than 2, no plaque and / or treadmill exercise test were negative for carotid artery ultrasound.  Exclusion Criteria:  (1) There was severe hepatic and renal insufficiency (2) Cancer and malignant disease patients (3) Severe acute infection or metabolic disorder (4) Acute attack of chronic heart failure (5) Acute myocardial infarction without revascularization within 2 weeks (6) Secondary to obvious valvular heart disease, hypertrophic obstructive heart disease