The etiology of ventricular septal defect is not fully understood and may be related to risk factors such as genetic factors, pregnancy-related diseases and exposure to drugs and toxins during pregnancy. Ventricular septal defect is a condition in which the ventricular septum is underdeveloped during the embryonic period and abnormal traffic forms between the left and right ventricles, producing a left-to-right blood shunt at the ventricular level. The etiology may be as follows: 1. Genetic factors: There is a family history of congenital ventricular septal defect. It is not uncommon for siblings to have the disease at the same time, or for parents and children to have the disease at the same time, and the nature of the disease is very similar. Animal experiments or human case-control studies have found that congenital ventricular septal defect is a polygenic genetic disease. Some studies suggest that the occurrence of the disease and the father is too old, consanguineous marriage is also related. 2, pregnancy disease factors: pregnant women with untreated and uncontrolled diabetes mellitus can cause a significantly higher risk of congenital ventricular septal defect in the fetus, but the risk decreases if the disease is controlled and stable in early pregnancy. The fetus is susceptible to the disease if the woman is infected with a virus during the first 3 months of pregnancy, especially from 3 weeks to 8 weeks of pregnancy. The risk of fetal morbidity is increased by colds, rubella virus infection, emotional stress or depression during pregnancy. 3, drugs and toxins during pregnancy: Pregnant women are exposed to teratogenic drugs such as lithium, phenytoin sodium or steroids in early pregnancy, which can lead to an increase in fetal morbidity. It has also been reported that taking aspirin, tetracyclines, birth control pills, application of sympathomimetic drugs and benzoylecgonine drugs in early pregnancy leads to the disease. The offspring of alcohol, marijuana, and exposure to chemical poisons, such as exposure to organic solvents, are susceptible to ventricular septal defects. Over-exposure to radioactive substances such as X-rays and isotopes in early pregnancy. In summary, ventricular septal defects are mainly caused by disturbances in the development of the heart of the embryo during early pregnancy and problems arising from impaired development of the ventricular septum. Therefore, it is important to pay attention to the prevention of related risk factors during pregnancy.