The heart is divided into four separate chambers. The upper chambers, or atria, are divided by a wall called the septum. An atrial septal defect (ASD) is a hole in that septum. Atrial septal defects are one of the most common heart defects seen.

When an atrial septal defect is present, blood flows through the hole primarily from the left atrium to the right atrium. This shunting increases the blood volume in the right atrium which means more blood flows through the lungs than would normally.

If left untreated, atrial septal defect may cause problems in adulthood. These problems may include pulmonary hypertension (which is high blood pressure in the lungs), congestive heart failure (weakening of the heart muscle), atrial arrhythmias (which are abnormal rhythms or beating of the heart) and an increased risk of stroke.