Atrial septal defect (ASD) is a hole in the wall between the two upper chambers of the heart, called the atria. This hole usually does not cause any symptoms or problems in a young child. Over a person’s lifetime, the extra blood crossing the hole goes to the lungs. This can damage the blood vessels of the lungs. Adults who still have a hole are at greater risk of strokes. If very small, an atrial septal defect may not require any treatment. Other defects may need cardiac catheterization or surgery to close or patch the hole.