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).

What causes ASDs?

Most congenital heart defects are likely caused by a combination of genetics and factors involving the mother while she is pregnant, such as use of alcohol and street drugs, as well as diseases such as diabetes, lupus and rubella. About 10 percent of congenital heart problems are caused by specific genetic defects.

How common are ASDs?

Atrial septal defects are the third most common type of congenital heart defect, and among adults, they are the most common. The condition is more common in women than in men.

What are the long-term effects of atrial septal defects?

Normally, the right side of the heart pumps blood that is low in oxygen to the lungs, while the heart’s left side pumps oxygen-rich blood to the body. When you have an ASD, blood from the left and right sides mix, and can keep your heart from working as well as it should.

If your ASD is larger than 2 cm, you have a greater risk of problems such as:

  • Right heart enlargement, which leads to heart failure.
  • Abnormal heart rhythms, including atrial fibrillation or atrial flutter, affect 50 to 60 percent of all patients over 40 with an ASD.
  • Stroke.
  • Pulmonary hypertension (high blood pressure in the arteries that supply blood to the lungs). Blood normally flows from the left side of the heart to the right, but having an ASD and severe pulmonary hypertension can cause the blood flow to be reversed. When this happens, oxygen levels in the blood drop, which leads to a condition called Eisenmenger syndrome.
  • Leaking tricuspid and mitral valves caused by an enlarged heart.

What are the symptoms of an ASD?

Many people have no idea they have an ASD because they do not have symptoms. Some patients find out about the defect when a chest X-ray for another problem shows that the right side of the heart is bigger than normal.

By age 50, an ASD can cause symptoms like shortness of breath, fainting, irregular heart rhythms or fatigue after mild activity or exercise.

Last reviewed by a Cleveland Clinic medical professional on 07/17/2019.



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  • American Heart Association. About Congenital Heart Defects Accessed 3/12/2015.
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  • National Heart, Lung, and Blood Institute. What are Congenital Heart Defects? Accessed 3/12/2015.
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