Tetralogy of Fallot is partly caused by chromosomal abnormalities, but there are also other causes, which are categorized into internal and external causes. 1. Endogenous causes: mainly related to heredity, such as chromosome ectopia and malformation, such as trisomy 21, trisomy 18, trisomy 13, trisomy 14 and trisomy 15. The incidence of Tetralogy of Fallot in children is also increased if the parents have congenital heart disease. 2. External causes: Intrauterine viral infections, especially rubella virus, mumps virus, coxsackie virus, etc.; exposure to large amounts of radiation during pregnancy, hypoxia, and advanced age of pregnancy, etc., can all contribute to the development of congenital tetralogy of Fallot. Tetralogy of Fallot is not necessarily caused by chromosomal abnormality. Patients should seek timely consultation and early treatment to avoid delaying the condition and affecting the prognosis.