The left-to-right shunt type of congenital heart disease is the most common type of congenital heart disease. As already mentioned, the main ones are atrial septal defect, ventricular septal defect, and patent ductus arteriosus. They are mainly caused by high pressure in the left side of the heart chambers and low pressure in the right side of the heart chambers. The following is an example of a ventricular septal defect with a left-to-right shunt. Under normal conditions, the left ventricle supplies blood to the whole body and does more work and has a higher pressure, usually up to 120 mmHg, which is the same as the value people usually measure when taking blood pressure. In patients with septal defect, when the heart contracts, there is a relatively large pressure difference between the left and right ventricles (120-20=100 mmHg). pressure difference (120-20=100 mmHg), blood flow goes from the left to the right. So how much blood flow has to go through? Let’s do a simple arithmetic problem. If a child has a septal defect of 4 mm and the echocardiographic velocity of the shunt is 4 m/s, how many shunts will there be in a minute? The area of the defect is 2 mm in radius, and the area is 2×2×3.14=12.56 mm2, and the flow rate per second should be multiplied by the bottom area and the flow rate of 4 m (4000 mm) (which is the shunt flow rate measured by echocardiography), that is 12.56*4000=50240 (mm3), within one minute (i.e. 60 seconds), there is only systolic shunt, and if the systolic period occupies If the systolic period accounts for 20 seconds, the flow rate per minute is 50,240×20=1004800mm3=1004.8cm3=1004.8ml, from which we can see that such a small hole, the flow rate per minute is still very large minion.