The left-to-right shunt causes the blood that should supply the whole body to shunt away from the septum midway, and the blood flow supplying the whole body is reduced. Due to the compensatory mechanism of the body, the heart has to work faster to adapt to the needs of the body. If the septal defect is large, the shunt flow is large and the pulmonary blood flow is high, it often causes lung infection, forming pneumonia and heart failure, which often requires injection and infusion or hospitalization; in less severe cases, the patient loses the opportunity for surgery because the pulmonary blood flow is too much and the overload shock of blood flow over the years forms resistance pulmonary hypertension, which is called Eisenmenger’s syndrome.