Ventricular septal defect (VSD) is the most common congenital heart disease, accounting for about 15%-25% of the total, excluding cyanotic congenital heart disease combined with ventricular septal defect. The septum is divided into membrane part and muscle part, and the muscle part is divided into inflow part, trabecular part and outflow tract (funnel part), and the trabecular part can also be divided into central, marginal and apical parts. (1) Perimembranous ventricular septal defect, also known as subcristal defect, accounts for 70% of the cases. The perimembranous ventricular septum is located under the aortic valve, and the perimembranous part extends from the membrane to the flow channel, outflow tract and myocardial trabeculae in contact with it. (2) Myocardial ventricular septal defect, accounting for 5%-20%, is divided into central, marginal and apical myocardial ventricular defects, with the central defect mostly located behind the regulating bundle and the apical defect adjacent to the apex, which is difficult to detect and repair. Marginal defects are often multiple, small and distorted, like Swiss cheese, and are very difficult to repair surgically. (3) Outflow tract (funnel part) is more common in oriental people, accounting for 20%-30%. The defect is located in the outflow part of the ventricular septum, which is part of the aortic and pulmonary valve annulus, also called supra-crural, sub-pulmonary valve or sub-arterial defect, and is easily complicated by prolapse and regurgitation of the aortic valve. (4) Inflow ventricular septal defect accounts for 5% to 8%, underneath the tricuspid septal valve, posterior and inferior to the perimembranous ventricular septal defect, lower part of the conical papillary muscle, between the mitral valve and tricuspid leaflet. The systolic pressure of the right ventricle in normal people is only 1/4 to 1/6 of that of the left ventricle, and the resistance of the pulmonary circulation is only about 1/10 of that of the body circulation, when there is a defect in the septum of the left and right ventricles, the blood of the left ventricle is shunted to the right ventricle. The size of the shunt flow depends on the size of the defect and the difference in resistance of the body-pulmonary circulation, thus producing different hemodynamic changes. (1) Small defects (Roger’s disease): defect diameter <5 mm or defect area <0.5 cm2/m2 body surface area. There is little left-to-right shunt flow at the ventricular level, little hemodynamic change, and may be asymptomatic. (2) Medium-sized defect: defect diameter 5-10 mm or defect area 0,5-1.0 cm2/m2 body surface area. The defect is larger, the fractional flow is more, the blood flow in the pulmonary circulation can reach 2 to 3 times that of the body circulation, and the pulmonary artery pressure is normal or mildly elevated. (3) Large defect: defect diameter >10 mm or defect area >1.0 cm2/m2 body surface area. A large amount of left-to-right shunt flow increases the blood flow in the pulmonary circulation, and the blood flow in the pulmonary circulation can reach 3 to 5 times that of the body circulation. When the capacity limit of the pulmonary vascular bed is exceeded, it produces dynamic pulmonary hypertension, spasm of the small pulmonary arteries, progressive thickening of the middle and intimal layers of the small pulmonary arteries, small lumen and obstruction, forming irreversible obstructive pulmonary hypertension. When the right ventricular systolic pressure exceeds the left ventricular systolic pressure, the left-to-right shunt reverses to a bidirectional shunt, or even a right-to-left shunt, and cyanosis develops clinically and becomes Eisenmenger syndrome. 3. Clinical manifestations Clinical manifestations depend on the size of the defect, pulmonary artery blood flow and pulmonary artery pressure. Small defects may be asymptomatic, generally unrestricted in activity, and growth and development are not affected. Medium to large defects can become symptomatic in the late neonatal period and infancy, with feeding difficulties, shortness of breath, pallor, excessive sweating, no weight gain, recurrent respiratory infections, and congestive heart failure often occurring within six months. Sometimes the dilated pulmonary artery presses on the recurrent laryngeal nerve, causing hoarseness. On physical examination, the cardiac border is enlarged, and a rough systolic murmur of III-IV can be heard between the third and fourth ribs at the left edge of the sternum, and systolic tremor can be felt as it conducts to the axilla. In high fractional flow, which leads to relative mitral stenosis, a softer mid-diastolic murmur can be heard in the apical region. In children or adolescents, large defects with significant pulmonary hypertension or Eisenmenger syndrome, cyanosis and pestle-like fingers (toes) appear, and the heart murmur is often reduced while the second pulmonary artery sound is significantly hyperactive. (1) Electrocardiogram may be normal in small defects; in medium defects, the electrocardiogram may show left ventricular hypertrophy with or without left atrial hypertrophy; in large defects, the electrocardiogram may show biventricular hypertrophy with or without left atrial hypertrophy; in the development of obstructive pulmonary hypertension or Eisenmenger’s syndrome, the electrocardiogram may show right ventricular hypertrophy only. (2) X-ray examination shows varying degrees of enlargement of the cardiac shadow, with enlargement of the left and right ventricles and the left atrium; the pulmonary artery segment is obviously prominent, and the pulmonary vascular shadow is thickened, the severity of which is proportional to the left-to-right shunt flow. In case of obstructive pulmonary hypertension or Eisenmenger syndrome, the main features are thickening of the main pulmonary artery branches and enlargement of the pulmonary hilum, while the peripheral pulmonary vascular shadow is very little, like a withered bald branch, and the cardiac shadow can be basically normal. (3) Two-dimensional echocardiography can accurately measure the anatomic location, size and number of defects and other associated malformations; Doppler echocardiography can also detect the size and direction of right and left interventricular shunts and estimate pulmonary artery pressure. (4) Cardiac catheterization is not required for simple ventricular septal defects. If combined with severe pulmonary hypertension, aortic valve prolapse, secondary right ventricular funnel stenosis or other cardiac malformations, cardiac catheterization is required. Cardiac catheterization can reveal a right ventricular oxygen level higher than 1 volume% of the right atrium, and can measure pulmonary artery pressure and calculate pulmonary circulation resistance. 5. Prognosis and complications (1) 30% to 40% of perimembranous and myocardial ventricular septal defects close spontaneously within 6 months, especially small defects. Ventricular septal defects do not increase in size with age, but rather decrease in size. Inflow defects and subpulmonary or bicuspid septal defects rarely close, and the latter are prone to aortic valve insufficiency due to aortic prolapse. (2) Congestive heart failure occurs within 6 to 8 weeks after birth in large ventricular septal defects. (3) Large ventricular septal defects can develop into obstructive pulmonary hypertension within 6 to 12 months after birth, but right-to-left shunts usually do not develop until the teenage years. (4) Large ventricular septal defects may develop secondary to funicular stenosis, which reduces the left-to-right shunt and even occasionally produces a right-to-left shunt (called atypical tetralogy of Fallot). (5) Occasionally, infective endocarditis may occur. (6) Treatment Because of the possibility of spontaneous closure of ventricular septal defects, small to medium sized defects can be followed up to preschool age. If respiratory infection and congestive heart failure occur in infancy, anti-infective, cardiotonic, diuretic, vasodilator and other medical management should be provided. In case of congestive heart failure that is difficult to control with drugs, repair should be performed within 6 months; after 1 year of age, if the ratio of pulmonary circulation/body circulation is greater than 2:1 with a large left-to-right shunt, repair should be performed promptly regardless of the pulmonary artery pressure. Surgery requires open-heart surgical repair under extracorporeal circulation with direct vision; since 2002, the eccentric Amplatzer ventricular septal defect sealer has been widely used in clinical practice, and interventional treatment has become the first choice. The indications are: ① perimembranous and myocardial ventricular septal defects; ② age is usually older than 3 years; ③ the diameter of the defect is 3 mm to 10 mm; ④ the distance between the defect and the aortic valve should be greater than 2 mm.