A congenital heart defect is a problem with the structure of the heart. It is present at birth. Congenital heart defects are the most common type of major birth defect.
A baby's heart begins to develop shortly after conception. During development, structural defects can occur. These defects can involve the walls of the heart, the valves of the heart and the arteries and veins near the heart. Congenital heart defects can disrupt the normal flow of blood through the heart.