Anemia causes myocardial ischemia because the heart has a very high oxygen requirement, second only to the brain, and all energy supply to the heart muscle comes from oxygen carried by red blood cells. Medically coronary atherosclerotic heart disease, also known as coronary heart disease, congenital heart disease, and rheumatic heart disease, is also called anemic heart disease. If the patient has a long-term chronic anemia, the heart muscle is kept in a long-term chronic hypoxic process. If after a short period of 1-2 days, 1-2 weeks, 1-2 months after the oxygen supply or anemia is restored, the myocardium can mostly recover. However, if anemia is present for 1-2 years or even 5-10 years, anemic heart disease can occur. Patients will show enlarged heart, decreased contraction of heart muscle, and feel chest tightness, weakness, palpitations, and even difficulty in breathing and shortness of breath with slight activity. So anemia definitely has damage to the heart muscle, mainly including the following two points: 1. duration of anemia: the longer the duration of anemia, the more damage to the heart muscle; 2. degree of hematocrit decrease: for example, the damage to the heart muscle is different between patients with hematocrit 3-4g/dL and 7-8g/dL, and the damage to the heart muscle is more serious with hematocrit 3-4g/dL. Patients with anemia around hematocrit 3g/dL who climb stairs or go running on the playground are likely to suffer sudden death, and the heart of such patients can suffer from pernicious arrhythmias or cardiac arrest. If the hematocrit is 7-8g/dL patients, the chance of sudden death will certainly be significantly reduced, but it is not impossible to happen. Very critical heart disease can also occur if the activity level reaches 1500m or 3000m of running. Therefore, anemia is a serious damage to the heart and must be taken seriously.