An ST-segment change in the ECG generally refers to an upward or downward shift of the ST-segment, reflecting the electrical activity of the heart muscle. ECG ST-segment changes can be clinically classified into two categories: ST-segment elevation may be myocardial infarction and ST-segment depression suggests the possibility of myocardial ischemia.1. ST-segment elevation: If a patient has at least two adjacent leads with ST-segment elevation of more than 0.1 mV, alert the patient to the possibility of acute ST-segment elevation myocardial infarction. If a patient has chest pain plus ST-segment elevation, he or she should go to the hospital at the first time to improve cardiac enzymes, troponin and other tests to confirm the diagnosis. In addition, we should also look at the dynamic evolution of the ECG. If ST-segment elevation is not seen on the ECG in a quiet state, but dynamic ST-segment elevation occurs during activity or emotional excitement, it means that the patient may have acute coronary infarction or acute spasm of the coronary artery, which is a very serious situation and must be taken seriously. 2. ST-segment depression: If there are at least two adjacent leads with ST-segment depression of more than 0.05 mV, the patient may have myocardial ischemia. If the ST-segment depression occurs after activity or emotional excitement, the possibility of ischemia is very high and is likely to be caused by moderate to severe stenosis of the coronary arteries. Some electrocardiograms show fixed ST-segment depression, which may be due to ischemia or left ventricular hypertrophy with strain. In addition to further improvement of the examination to clarify the presence of coronary stenosis, blood pressure should be monitored and cardiac ultrasound should be performed to clarify the presence of structural abnormalities of the heart muscle.