st wave changes include prolonged time limit, depression greater than normal, elevation greater than normal. 1. Prolonged time limit: the normal time limit is 0.05~0.15s, prolonged time limit can be seen in hypokalemia, greater than 0.16s. 2. Depression greater than normal: the normal st segment is located on the isoelectric line, and the downshift of all leads is not more than 0.05mv, and greater than normal value is commonly seen in myocardial ischemia, myocardial damage, and ventricular hypertrophy. 3. Elevation greater than normal: under normal circumstances, the st segment elevation of all limb leads and V4~V6 leads does not exceed 0.1mv, and the elevation of V1~V2 leads does not exceed 0.3mv. Elevation greater than normal can be seen in acute myocardial infarction, acute pericarditis, and angina pectoris. When the st segment changes, you should consult a doctor in time, and the professional doctor will take the appropriate treatment according to the clinical symptoms and other comprehensive analysis.