Fa IV is the most common complex congenital heart disease, with a large number of surgeries every year, but the mortality rate is still not low, for many reasons of course, but the main risk comes from the developmental condition of Fa IV. Normal human blood circulation can be seen as a share of blood circulating constantly in a vascular ring, right heart, pulmonary artery, pulmonary vein, left heart, aorta, body vein, right heart, without traffic with each other, as if four cars were running constantly in a ring of four lanes. So what does the patient’s circulation look like in Law 4? Let me put it metaphorically, because of the pulmonary stenosis, only 2 of the 4 cars from the right heart may go to the pulmonary artery, and 2 cars go directly to the left heart through the ventricular septal defect. A normal person has 4 cars of oxygen, but a patient with law 4 has only 2 cars of oxygen, so there is not enough oxygen and he will be cyanotic and have purple lips. Pulmonary artery because there are only 2 cars, its lane does not have enough stimulation to keep 2 lanes, and does not develop, after the root, 4 cars can only go to the pulmonary artery, when the 2 lanes of the pulmonary artery can not bear, the patient will not live. This is why we have to look at the chest X-ray, look at the CT, look at the angiography to assess the development of the pulmonary artery, the better development of, for example, have 3 lanes, postoperative will be good to pass. If the development is not good you can do a B-T shunt to stimulate the development of the pulmonary artery before radical treatment. In addition to the development of the pulmonary artery, there is another indicator that is particularly important, and that is the collateral circulation. The collateral circulation is some abnormal vessels from the aorta to the pulmonary artery, which is a kind of self-protection of the body, formed gradually due to hypoxia, to provide more blood to the pulmonary circulation for oxygenation, and there is no collateral circulation in normal people. This collateral circulation is great preoperatively, but for postoperatively it is a major weapon. Even if the pulmonary artery is 3 lanes, after radicalization, 4 cars in the right heart plus 1 car in the collateral circulation, 5 cars going 3 lanes is dangerous. So there is a preoperative go to block the collateral circulation to improve the success rate of surgery. Having said that, there are actually two points: pulmonary artery development and collateral circulation. The success rate of surgery will be high if these two points are clear.