An atrial septal defect (ASD) is a congenital heart defect in which the wall that separates the upper heart chambers (atria) does not completely meet and close, thus leaving a hole or defect (hole-in-the-heart).
Blood is then able to flow from the left to the right atrium. This is called a shunt. If too much blood moves to the right side of the heart, blood pressure in the lungs may build up and cause irreversible damage. Many problems can occur if the shunt is large, but small atrial septal defects often cause very few problems and may be found much later in life.

When the patient has no other congenital defect, symptoms may be absent, particularly in children. Symptoms may begin any time after birth through childhood and even in adulthood. Patients with an ASD are at an increased risk for developing a number of complications including:

1. Atrial fibrillation (in adults)
2. Right heart failure
3. Pulmonary overcirculation
4. Pulmonary hypertension
5. Stroke.

A procedure has been developed to close the defect without surgery. This involves placing an ASD closure device into the heart through tubes called catheters. The cardiologist makes a tiny surgical cut in the groin, then inserts the catheters into a blood vessel and up into the heart. The closure device is then placed across the ASD and the defect is closed.