Cyanosis is a manifestation of human hypoxia. If the reduced hemoglobin in human body is lower than 50g/L, it can carry 20ml% of oxygen and the oxygen saturation is 95% to 100%; if the reduced hemoglobin in blood is higher than 50g/L and the oxygen saturation of body artery is lower than 85%, the skin, fingers, toes, nail bed and mucous membrane show blue or purple-black color, which is clinically called cyanosis. The causes of cyanosis are: abnormal hemoglobin and excessive amount of reduced hemoglobin. Cyanosis in congenital heart disease is due to an increase in reduced hemoglobin. What are the conditions in which cyanosis can occur? Some children with congenital heart disease have cyanosis after birth, such as pulmonary valve atresia, permanent arterial trunk, tetralogy of Fallot, complete transposition of the great arteries, tricuspid atresia, complete pulmonary vein ectopic drainage and other malformations, and there is a “right-to-left” shunt of blood inside the heart, so that venous blood with low oxygen content enters the body circulation without oxygenation, resulting in The increase of reduced hemoglobin content leads to cyanosis, which is called central cyanosis. 2. Some congenital heart diseases are born without cyanosis, but with the development of the disease, pulmonary hypertension occurs, resulting in the shunting of blood from the left atrium, left ventricle or aortic system to the right atrium, right ventricle or pulmonary circulation (“left-to-right” shunt) to the right atrium, right ventricle or pulmonary artery system to the left atrium, left ventricle or body circulation (“right-to-left” shunt). “right-to-left” shunt), and cyanosis occurs. 3. In patients without shunts, cyanosis may also occur due to heart failure, poor oxygenation of blood in the lungs, and slow flow of blood in the tissues, resulting in the exchange of more oxygen from the blood to the tissues and an increase in reduced hemoglobin, called peripheral cyanosis. Clinically speaking, the heavier the cyanosis is, the more serious the disease is, especially in congenital heart disease without cyanosis before, if cyanosis appears, it indicates that the disease has developed to an advanced stage and the time for surgery is likely to be lost. Therefore, we should pay close attention to the time of cyanosis appearance and the trend of change, and for non-cyanotic patients, we should also operate as early as possible to avoid losing the opportunity of surgical treatment when cyanosis appears. 1, Because the blood flow from intracardiac malformation into the lung is reduced and the oxygenated blood volume cannot meet the metabolic requirements of the body, so the body compensates to the lung tissue and bronchus to produce extensive neovascularization, i.e. collateral circulation, in order to increase the blood flow into the lung and ensure the oxygen demand of the body, these abnormal collateral vessels easily rupture into the trachea and produce coughing up blood. 2. On the other hand, congenital heart disease with a large shunt from the body circulation to the pulmonary circulation, due to a large increase in pulmonary blood flow, resulting in pulmonary hypertension, organic lesions, and cyanosis occurring in the late stage with a shunt from the pulmonary circulation to the body circulation. Due to pulmonary hypertension, the pulmonary vessels become thin and easily rupture, and blood is coughed out through the trachea, which is manifested as coughing up blood. Once a cyanotic patient coughs up blood, the first thing to do is not to panic, and the patient should be placed at rest and sent to the nearest hospital for medication or surgery. These patients should usually pay attention to no strenuous activities and try to eat soft food to avoid the occurrence of infection.