Unstable angina is a more serious type of angina in coronary artery disease, mainly caused by ischemic changes in the heart due to narrowing or occlusion of coronary arteries. Unstable angina can be divided into resting angina, primary angina and worsening angina according to the severity and onset characteristics. The symptoms of angina pectoris in general refer to a crushing or tightening pain behind the sternum, which may radiate to the back, left upper limb and neck, accompanied by chest tightness and panic, and can be relieved by taking quick-acting heart pills or nitroglycerin. Generally, the duration of chest pain is between 15-30 minutes, mostly less than 30 minutes. The symptoms of angina can be triggered by exertion, emotional excitement, cold, stimulation, etc.