Some children with simple precordial disease (atrial defect, ventricular defect, and patent ductus arteriosus) who develop pulmonary hypertension due to delayed treatment are expensive to treat later and have poorer outcomes. Therefore, early detection and early surgical treatment are necessary for these children. The mechanism of pulmonary hypertension can be understood as the change in the internal diameter of the pulmonary vessels. If the internal diameter is counted as 10 parts, it can be said that 5 parts are used to maintain vital signs and 5 parts are reserved for compensatory reserve. When the pulmonary vasculature contracts, the internal diameter becomes smaller and the reserve is used. If there are anatomical changes in the pulmonary vasculature, such as thickening of the vessel wall due to long-term pulmonary hypertension, which is a non-recoverable factor, the pulmonary vascular internal diameter becomes smaller and then the reserve is diminished, and in fact a small change in the pulmonary vasculature can lead to fatal pulmonary hypertension crisis. In pediatric patients with some precordial diseases, due to hemodynamic changes, the blood in the lungs increases, gradually causing the formation of pulmonary hypertension. This process is prone to pneumonia causing fever, hypoxia, high carbon dioxide, and acidosis leading to pulmonary vasoconstriction and the occurrence of fatal pulmonary hypertension crisis. In these children, preoperative cardiac catheterization should be done to see how much pulmonary vascular reserve is left in order to clarify the treatment before and after cardiac surgery. In conclusion, the direct risk factors of pulmonary hypertension include strong reduction of pulmonary vascular lumen diameter, reduced left heart preload, increased right heart afterload, low volume of body circulation, low perfusion, sudden right heart expansion, acute right heart insufficiency, and arrhythmia. Indirect hazards are seen in the side effects of shock and hypoxia on the organism. Therefore the prevention and treatment of pulmonary hypertension is more important than the treatment! It is better to eliminate the factors that can cause pulmonary hypertension to the maximum extent in the perioperative period than to deal with it when it appears. In the case of preoperative pulmonary hypertension with cardiac catheterization, for better postoperative recovery, preoperative pulmonary hypertension is usually treated for 1-3 weeks, mainly with low-flow oxygen, prostaglandin E, sildenafil, captopril combination therapy, absolute sedation and analgesia during postoperative monitoring, ventilator hyperventilation (PaCO2 30mmHg or so), maintaining high partial pressure of oxygen (higher oxygen concentration) as much as possible, and dilatation. high oxygen concentration), vasodilators (prostaglandin E, nitroprusside, bosentan, nitroprusside), good maintenance of the internal environment, inotropes, NO inhalation, etc. The drug can be gradually withdrawn when the heart function recovers enough to counteract the high pulmonary pressure.