Atrial Septal Defect



An atrial septal defect (ASD) is a hole in the “wall” (septum) that separates the heart’s two upper chambers (atria). The hole is caused by abnormal development of the wall leading to missing tissue in the wall. According to the Centers for Disease Control and Prevention (CDC), about 1 in every 2,000 babies born in the U.S. each year is born with ASD.1

An illustration demonstrating an atrial septal defect

The patent foramen ovale (PFO) is actually a normal communication in the atrial wall. It acts more like a one-way valve shunting blood from the right atrium to the left during fetal life, bypassing the lungs because the fetus doesn't breathe. After birth, the baby takes the first breath and the physiology changes where the pressure in the left atrium rises above the right atrium and the valve-like structure closed the communication. Over time, the valve fuses with the wall, and the communication is permanently closed. However, in 25%–30% of adults, the fusion isn't complete and can still open up with the right atrial pressure rising above the left atrium in certain conditions such as bearing down or coughing.

Very small ASDs have been known to close by themselves spontaneously. Moderate and larger ASDs will likely persist into adulthood unless treated.

A hole in the septum allows blood to cross from the heart’s left atrium to the right atrium. When this happens, blood that has just returned to the left atrium from picking up oxygen in the lungs will cross to the right atrium. From there, it returns to the lungs without traveling through the body first. The result is inefficient blood circulation and increased blood going to the right side of the heart and lungs.

If the ASD is small, blood flow into the right side of the heart and the lungs may not significantly increase. Larger holes, though, can allow much more blood to flow to the right heart and lungs, leading to enlargement of the right-sided heart chambers. This may result in the development of abnormal heart rhythms (arrhythmias); abnormal elevation in the blood pressure in the lung arteries (pulmonary hypertension); and, in some cases, symptoms of congestive heart failure.

    Atrial septal defect animated primer

    Watch the animated video to learn more about how atrial septal defect affects the body.

    Baby and stethoscope

    Children's Heart Health

    Information for parents of children with pediatric heart conditions. Read more about conditions, tests, and treatments for congenital heart disease.

    Stories of Hope and Recovery

    Anna Grace Bundros

    Patient Story: Anna Grace receives catheter-based treatment for atrial septal defect with care from an interventional cardiologist.  

    Anna Grace Bundros patient of Dr. Dennis Kim