Atrial Septal Defect (ASD)

An atrial septal defect (ASD) is a hole in the part of the septum that separates the atria. (The atria are the upper chambers of the heart.)

An ASD allows oxygen-rich blood to flow from the left atrium into the right atrium, instead of flowing into the left ventricle as it should. So, instead of going to the body, the oxygen-rich blood is pumped back to the lungs, where it has just been.

Cross-Section of a Normal Heart and a Heart With an Atrial Septal Defect

Atrial Septal Defect Anatomy

Figure shows the normal structure and blood flow in the interior of the heart. Figure B shows a heart with an atrial septal defect. The hole allows oxygen-rich blood from the left atrium to mix with oxygen-poor blood from the right atrium.

  • Your heart has two sides, separated by an inner wall called the septum. An atrial septal defect (ASD) is a hole in the upper part of the septum, which separates the atria.
  • Atrial septal defects allow blood to pass from the left side of the heart to the right side. This means that oxygen-rich blood can mix with oxygen-poor blood. As a result, some oxygen-rich blood is pumped to the lungs instead of out to the body.
  • Atrial septal defects can be small or large. Many small ASDs close on their own as the heart grows during childhood. Large holes in the septum are less likely to close on their own over time.
  • A heart murmur (an extra or unusual sound heard during a heartbeat) is the most common sign of both ASD. If an ASD causes heart failure, signs and symptoms may include fatigue (tiredness), tiring easily during physical activity, shortness of breath, a buildup of blood and fluid in the lungs, and a buildup of fluid in the feet, ankles, and legs.
  • Many babies who are born with atrial septal defects have no signs or symptoms.
  • Doctors usually diagnose holes in the heart based on results from a physical exam and tests and procedures. The exam findings for an ASD often aren't obvious, so the diagnosis sometimes isn't made until later in childhood or even adulthood.
  • Many holes in the heart don't need treatment, but some do. Most holes in the heart that need treatment are repaired in infancy or early childhood. Sometimes, adults are treated for holes in the heart if problems develop.
  • The treatment your child receives depends on the type, location, and size of the hole. Other factors include your child's age, size, and general health. Holes in the heart are treated with catheter procedures or surgery.
  • The outlook for children who have ASDs is excellent. Advances in treatment allow most children who have these heart defects to live normal, active, and productive lives with no decrease in lifespan.
  • Many children who have atrial septal defects need no special care or only occasional checkups with a cardiologist (heart specialist) as they go through life.

What Causes Atrial Septal Defects?

Mothers of children who are born with atrial septal defects (ASDs) or other types of heart defects often think that they did something wrong during the pregnancy to cause the problems. However, most of the time, doctors don't know why congenital heart defects develop.

Heredity may play a role in some heart defects. For example, a parent who has a congenital heart defect is slightly more likely than other people to have a child with the problem. Very rarely, more than one child in a family is born with a heart defect.

Children who have genetic disorders, such as Down syndrome, often have congenital heart defects. Half of all babies who have Down syndrome have congenital heart defects.


Reference: The National Heart, Blood, and Lung Institute

Last updated February 20, 2020

This information is for general educational uses only. It may not apply to you and your personal medical needs. This information should not be used in place of a visit, call, consultation with or the advice of your physician or health care professional.

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