What Is Atrial Septal Aneurysm?

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The atrial septum is a membrane between the left and the right upper chambers of the heart, which are called the atria. It normally separates them. But the atrial septum also can weaken and bulge, creating an aneurysm that causes it to malfunction.

An atrial septal aneurysm (ASA) is one cause of stroke, a potentially life-threatening blockage of blood flowing to the brain. It is linked to what are called cryptogenic strokes. The cause of these strokes is unclear, but they are associated with genetic heart conditions like mitral valve prolapse, or abnormal heart rhythms like atrial fibrillation.

This article looks at how an ASA is linked to having a stroke, but also its connection to other health issues. It also discusses how this aneurysm may be treated.

Woman caressing ill man in hospital ward
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The heart has four chambers, with two atria above two ventricles. These four spaces are defined by whether they are on the right or left side of the heart. Normally, the septum separates the left and right atria.

Sometimes, though, the septum pushes into the atrial spaces themselves every time the heart beats. This defines an ASA. It keeps the heart from working properly, and from pumping back out all of the blood that returns to the right atria from the body.

The condition increases the risk of stroke or a transient ischemic attack (TIA), a kind of mini or "warning" stroke. Strokes have many symptoms of their own that include:

  • facial drooping
  • speech changes
  • difficulty moving or walking
  • vision changes
  • change in mental status
  • headaches

These are signs of a serious health condition and they require immediate medical help. But they are not the same thing as the symptoms of an ASA itself; these include symptoms similar to those seen in other congenital heart defects, such as shortness of breath or fatigue.

In fact, there may be no symptoms at all, because this aneurysm is usually found through an echocardiogram or other imaging technique. It appears as an unusually large and bulging membrane that moves between the two atria of the heart.


Up to 40% of all strokes have no known origin. These cryptogenic strokes, as they are called, often are linked to heart defects that people have had since birth. Atrial septum aneurysms also may be linked to these congenital heart conditions.


An ASA often is linked to another heart defect, the patent foramen ovale (PFO) of the heart. This is commonly known as a "hole" in the heart wall. It exists while a fetus is developing, but it usually closes at birth when a baby starts breathing on its own.

In people with a PFO, the hole never closes the way it should. The condition happens in about 25% of the population and many of them have no serious problems. Still, the hole in the heart wall allows blood to pass between the chambers, and an already weakened septum can develop the aneurysm. In fact, ASA is far more rare but it's linked to PFO in at least 60% of cases.

A September 2021 review looked at 12 studies to evaluate these kinds of atrial septal abnormalities, and to better see the link between atrial issues and cryptogenic stroke. The risk of stroke was higher in people with ASA, as well as those with atrial fibrillation heart rhythms. But the study wasn't definitive, with the authors noting only that these atrial weaknesses may cause stroke.


Imaging is key to an ASA diagnosis, and in many cases a complete echocardiogram of the heart may be done if a person has a related congenital heart condition. It also may be done if someone has a stroke and doctors are trying to find out why. They may look for blood clots in the left atrium, a PFO, a mitral valve prolapse, or the ASA.

The person's overall health and family history also are needed for a complete diagnosis. That's especially true if the person has a history of strokes, TIAs, or other cardiovascular issues.


There are two main pathways for treating ASA. First, it may seem obvious to just surgically close a PFO because there's such a strong link between the congenital defect and the ASA. But many people are fine with a "hole" and doctors continue to disagree about the benefits of such surgeries.

Second, if a doctor thinks a person with an ASA is at risk for stroke, or already had one, they may want to try drugs that prevent blood clots and other strategies that will limit the stroke risk.


For many people, an ASA may happen because they already had an underlying condition at birth. They may not even notice it for a long time. But it does increase the chance of having a stroke, so it's important to know the signs and symptoms.

If you have concerns about a congenital heart problem and its risks, let your doctor know.

A Word From Verywell

If you're learning about an ASA, it may be because you have a congenital heart condition. There's a good chance that you've lived your life without it being a big deal, and that you didn't even know there may be a health risk because of your "minor" heart issue.

But there are other risks, and an ASA may be a part of them. So don't forget to tell your family, and your doctor, about any health issue that you've become so used to that you don't even think it matters. It does.

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  1. Centers for Disease Control and Prevention. Stroke Signs and Symptoms. Reviewed August 28, 2020.

  2. Razaq M, Parihar RK, Saini G. Atrial septal aneurysm and stroke. Ann Pediatr Cardiol. 2012;5(1):98-9. doi:10.4103/0974-2069.93726

  3. Ioannidis SG, Mitsias PD. Patent foramen ovale in cryptogenic ischemic stroke: direct cause, risk factor, or incidental finding? Front Neurol. 2020;0. doi: 10.3389/fneur.2020.00567

  4. Sun H, Zhou C, Xu L, Xu T. A meta-analysis of the association of atrial septal abnormalities and atrial vulnerabilityMedicine. 2021;100(35):e27165. doi: 10.1097/md.0000000000027165

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