The pathophysiologic changes in the biventricles of ventricular septal defects depend on the size of the defect and the resistance of the pulmonary arteries. If the diameter of the defect is less than 5 mm, it is a small-sized ventricular septal defect, and the blood flow shunted from left to right is less, which does not have much effect on the biventricles. If the diameter of the defect is 5-10 mm, it is a medium-sized ventricular defect, the left-to-right shunt blood flow increases, and the pulmonary blood flow can be more than 1.5 times of the blood volume of the body circulation, but it does not exceed the reserve capacity of the pulmonary vascular bed, and the pulmonary vascular resistance can be unincreased for a long period of time, and then it shows the left ventricular hypertrophy, and the left atrium, the left ventricle, and the right ventricle increase in blood flow. When the diameter of the defect is greater than 10 mm for large ventricular septal defects, left to right shunt blood flow, so that the pulmonary circulation blood flow exceeds the reserve capacity of the pulmonary vascular bed, will soon appear obstructive pulmonary hypertension, resulting in biventricular hypertrophy and dilatation, when the right ventricular pressure exceeds the left ventricle will appear bruising.