The difference between unstable angina and non-ST-segment elevation myocardial infarction is still relatively large, because unstable angina is a prelude to myocardial infarction. Once unstable angina occurs, the patient will experience a feeling of tightness, pressure, and cramping behind the sternum, while prolonged unstable angina will result in myocardial infarction. In contrast, non-ST-segment elevation myocardial infarction is a very serious type of myocardial infarction in which irreversible damage to the myocardium occurs in the presence of prolonged angina, leading to myocardial necrosis. Treatment is mainly due to conservative treatment with medications, coronary stenting and surgical open-heart bypass surgery, all of which can relieve the symptoms of angina or myocardial infarction.