Unknown cause: We don't know the exact cause of most heart defects. Although the reason defects occur is presumed to be genetic, only a few genes have been discovered that have been linked to the presence of heart defects. So they're likely due to a combination of multiple genetic and environmental factors. There's usually a 2 to15 percent chance of a heart defect happening again in the family. The odds depend on what type of defect you have and whether anyone else in your family has a heart defect.
Genetic syndrome: Some people with congenital heart defects have a specific genetic condition that can include other health problems. They may or may not know that they have such a condition. The chance for their child to also have this condition can be as high as 50 percent. These conditions can vary widely in their severity, so children may have less serious or more serious health problems than their parents. Learn more about genetic counseling.
Single gene: Rarely, congenital heart defects are caused by changes in a single gene. Often when this is the case more than one person in the family has a heart defect. The chance for another family member to have a heart defect can be as high as 50 percent.
Environmental exposure: Heart defects can also be caused by something your mother was exposed to in her pregnancy with you, such as an infection or a drug. In this case, the chance that your children will have heart defects is no higher than that of the average person.