Angina pectoris is not a blockage of blood vessels, but is caused by acute and temporary ischemia and hypoxia of the myocardium due to insufficient coronary blood supply. It is characterized by episodic pressure pain in the precordial region, mainly located behind the sternum, can be radiated to the precordial region and the medial side of the left upper limb, lasting from a few seconds to a few minutes, and the symptoms disappeared after resting or taking nitroglycerin. Pathogenesis of angina pectoris: any cause of coronary artery blood supply and myocardial blood demand contradiction between the coronary artery blood flow can not meet the needs of myocardial metabolism, resulting in myocardial acute, temporary ischemia and hypoxia, that is, angina pectoris occurs. The specific causes of angina pectoris are as follows 1. Atherosclerosis caused by coronary artery stenosis or part of the branch occlusion, its dilatation is weakened, when the cardiac load suddenly increased, such as fatigue, agitation, left heart failure systolic blood pressure increases, heart rate accelerated, the myocardial blood demand increases. 2. Blood flow is further reduced when spasm occurs in the coronary arteries. 3. In the case of a sudden decrease in circulating blood flow, the contradiction between myocardial blood oxygen supply and demand deepens, thus causing angina pectoris. If angina symptoms are not relieved after rest or nitroglycerin observation, you should go to the hospital immediately to avoid delay.