An atrial septal defect is an opening in the wall that separates the upper chambers of the heart. It is one of the most common congenital heart defects, which are structural problems that develop before a baby is born or at birth.

When an atrial septal defect is present, some oxygen-rich blood that should have been pumped to the body flows from one side of the heart to the other. This blood is then pumped to the lungs. This creates extra work for one side of the heart.

If an atrial septal defect is large, heart failure may occur, although this is not common in children. Many children have no symptoms. So this defect may not be found until a child is older or becomes an adult.

A heart catheterization can typically be used to close the opening. This prevents blood from flowing between chambers.