Doctors don't know what causes most cases of tetralogy of Fallot and other congenital heart defects.
Certain conditions or factors that occur during pregnancy may raise your risk for having a child with tetralogy of Fallot. These conditions and factors include:
Heredity may play a role in causing tetralogy of Fallot. An adult who has tetralogy of Fallot may have an increased chance of having a baby with the condition.
Children who have certain genetic disorders, such as Down syndrome and DiGeorge syndrome, often have congenital heart defects, including tetralogy of Fallot.
Scientists continue to search for the causes of tetralogy of Fallot and other congenital heart defects.