What is an Atrial Septal Defect?

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  • Written By: wiseGEEK Writer
  • Edited By: Niki Foster
  • Last Modified Date: 14 November 2019
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The heart is divided into four chambers. The septum or wall separates the top two chambers, called the atria. In some cases, a portion of this wall fails to form in the fetal heart. The result is an atrial septal defect (ASD).

All infants have a small opening in their atria right after birth, called a foramen ovale. Sometimes, as the fetal heart forms, lower pressure in the right heart causes the left atrium to send more blood through the foramen ovale, creating a larger than usual hole. While the normal foramen ovale closes shortly after the baby is born, this larger hole may not close and is termed an atrial septal defect.

An atrial septal defect is classified by the position of the hole in the septum, as well as by size. When the hole is in the middle of the septum, it is called a sinus venosus defect. A hole in the lower part of the septum is termed an ostium primum, and one at the top of the septum is an ostium secondum.


Septal defects of the atria and ventricles are the most common of all heart defects. Often, an atrial septal defect is so small that it will close on its own and never require surgery, as is the case with a small foramen ovale. In some cases, however, the size of the atrial septal defect causes the right atria to become larger, and also enlarges the pulmonary valve. It can affect the way a child grows and cause fatigue as well.

Diagnosis is usually made when a heart murmur is heard by the child’s pediatrician. A pediatric cardiologist then performs an echocardiogram to determine both the position and size of the atrial septal defect. Unless the atrial septal defect is very large, a prenatal ultrasound will probably not catch this defect, and even fetal echocardiograms do not often see ASDs.

Treatment depends upon the size of the hole and whether there are other heart defects present. Sometimes in sinus venosus, there is an anomaly of the pulmonary veins in which some of them connect to the wrong ventricle. In atrioventricular canal, the ASD is actually a complete absence of the septum and requires immediate surgical attention.

Fortunately, even if an atrial septal defect does not close on its own, it may not need to be addressed through surgery. Experimentation with catheters has led to using an umbrella-like patch, which is affixed to the atria to close small holes. When this is not possible, surgery is generally short and has an excellent success rate. A person with a repaired atrial septal defect has a normal life expectancy and no restrictions on activity after recovery.


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Post 1

I was recently diagnosed with an atrial septum anuerysm with no other remnarkable factors. Can I lead a normal lifestyle? And what can I do to improve the condition? Thanks

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