What is an atrial septal defect (ASD)?

What is an atrial septal defect (ASD)?

An atrial septal defect (ASD) is a hole in the septum, which is the muscular wall that separates the heart’s two upper chambers (atria). An ASD is a defect you are born with (congenital defect) that happens when the septum does not form properly. It is commonly called a “hole in the heart.”

A secundum ASD is a hole in the middle of the septum. The hole lets blood flow from one side of the atria to the other. The direction depends on how much pressure is in the atria.

More complicated and rare types of ASDs involve different parts of the septum and abnormal blood return from the lungs (sinus venosus) or heart valve defects (primum ASDs).