Myocardial ischemia is caused by a relative or absolute shortage of blood supply to the myocardium due to a decrease in myocardial blood supply and oxygen supply or an increase in myocardial oxygen demand. Myocardial ischemia can be seen in various causes of conflict between coronary blood supply and myocardial blood demand, so that coronary blood flow cannot meet the needs of myocardial metabolism. The common causes of myocardial ischemia are as follows: 1. Reduced myocardial blood and oxygen supply: The direct cause of myocardial ischemia is coronary artery atherosclerosis, severe luminal narrowing, and insufficient establishment of collateral circulation, which reduces or interrupts blood supply and causes severe and persistent myocardial ischemia, local myocardial ischemia and even necrosis. It mostly occurs in atherosclerotic coronary arteries, especially due to certain factors that cause atherosclerotic plaques to rupture and platelets to gather on the surface of the ruptured plaques, forming thrombi and blocking the lumen; or severe and persistent spasm of coronary arteries that interrupt blood flow. Other causes include coronary artery embolism and aortic valve lesion, which can cause blood vessel narrowing and lead to insufficient blood supply to the heart. 2, increased myocardial oxygen demand: a dramatic increase in myocardial oxygen consumption can lead to an imbalance in blood flow supply and demand ratio, which can also cause myocardial ischemia. Overwork, excitement, cold, overeating, constipation, alcohol consumption, severe arrhythmia, and dramatic rise in blood pressure can increase myocardial oxygen demand. Myocardial ischemia occurs when the blood and oxygen supply to the myocardium cannot meet the increase in oxygen demand. 3. Anemia, severe hypoxemia, severe aortic stenosis and other diseases can also lead to myocardial ischemia. Decreased myocardial blood supply and oxygen supply or increased myocardial oxygen demand can lead to the occurrence of myocardial ischemia. Prevention of atherosclerotic diseases is the most effective measure to prevent myocardial ischemia; patients with coronary heart disease need to avoid overwork, excitement, constipation and other triggers that aggravate myocardial ischemia.