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Atrial Septal Defect



An Atrial Septal Defect (ASD) is a congenital heart condition (i.e. something you were born with). An ASD is a hole within the wall that separates the upper chambers of the heart. This wall is known as the atrial septum, and it separates the right and left atria.

The size of the hole - or “Defect” - can vary from being as small as a pinhead to as large as a golf-ball. The importance of the hole and the effect it has on the heart is closely tied to its size.


In normal adult circulation, de-oxygenated blood first enters the right side of the heart. It is then guided to the lungs where it picks up the oxygen that we breathe in. The now oxygenated blood returns to the left side of the heart and is subsequently pumped out to the rest of the body.

The atrial septum is a muscular wall within the heart that separates the upper right and left chambers of the heart (the right and left atrium).


The septum prevents blood directed to the lungs (by right side of the heart) from being mixed with the blood directed to the body (by left side of the heart).


An ASD is a hole in this separating wall, and results in a greater flow of blood into the right side of the heart from the left atrium due to pressure differences. This happens because, almost always the pressure in the left atrium is higher than the pressure in the right atrium.

Over time, the right side of the heart will undergo structural changes due to an ASD. Such changes include:

  • Enlargement of the right side of your heart 

  • Extra Heart Beats or heart rhythm abnormalities 

  • Tricuspid Valve leakage (valve between right atrium and ventricle)

  • Pulmonary Hypertension (high blood pressure in the lungs)

Atrial Septal Defect

What does this mean for me?

Backpack Brick Analogy

Dr. Eric Horlick on Benefits of Closing the ASD.

Imagine that you are born with a backpack on your back -- you’ve never experienced life without it!

Living with an ASD is like adding a brick to your backpack every decade for the rest of your life. It would be unlikely that you would notice the increased physical load because of its gradual progression. Likewise, ASD symptoms develop slowly and progressively. You may attribute how you are feeling to age, weight gain, or lack of exercise.


While you may not notice an increase in symptoms as you age, we know that significant ASDs reduce exercise performance and cause alterations to the form and function of your heart. With time, some of these changes may become irreversible or only partially reversible. By closing your ASD we can permanently reduce the unnecessary load on the right heart.

Elderly Patients 

For patients under the age of 40, closing the ASD usually restores the right ventricle to normal size.


After the age of 40, while some patients' right ventricles will return to normal functioning, some will not. Despite this, we still expect the right ventricle to shrink substantially in size even if it does not normalize.


By restoring right ventricular structure and function we believe that treating patients before age 50 also serves a protective function, especially against the development of cardiac rhythm problems such as atrial fibrillation and atrial flutter.

Pregnant Patients 

In general, most women with an ASD can tolerate pregnancy without any significant problems. This should be considered on a case by case basis by involving a cardiologist who specializes in heart disorders of pregnancy.


However, patients with larger defects, who are symptomatic and with ASD-related complications such as arrhythmias or pulmonary hypertension may be at greater risk of developing complications during pregnancy.

Patients who have undergone ASD closure in the past, with no complicating features may generally go on to have uncomplicated pregnancies. It is very important to speak to your doctor about becoming pregnant if you have had or have an ASD. The information presented here is of a general nature only and should not be considered medical advice.

Health Implications


ASD Symptoms generally vary from patient to patient. In some cases, a patient with an ASD may not perceive any symptoms , while in other cases, they may have severe symptoms.

Many young people with an ASD feel that “I am just not a runner”, or “I have never been much of an athlete”, where in fact their life long exercise limitation may be attributed to their ASD. It is rare to find olympic caliber athletes with an ASD as having an ASD implies a reduction in potential cardio-respiratory function at peak.

Causes: Why do I have an ASD?

There is no single, absolute explanation that explains why some individuals are born with an ASD. Some genetic or inheritable conditions have a higher association with ASD formation. For example, patients with Down Syndrome or Holt-Oram Syndrome have a higher incidence of ASD.

NOTE:  While individuals with down syndrome or other genetic predispositions may have an ASD associated with their condition, the reverse is not true. In other words, just because you have an ASD, does not mean you have a rare genetic syndrome.

Long Term Health Implications of ASD

In the heart, the left atrium is more pressurized than the right atrium because the left side of the heart needs a great amount of pressure to eject blood out to the rest of the body.

As a result, blood flows through the ASD from the left side of the heart to the right side. This increases the volume of blood pooled in the right chambers of the heart which leads to the compensational enlargement of the right side of the heart - specifically the right ventricle. This can lead to the following complications:

Next Steps

The following symptoms  and signs are associated with but are not exclusive to ASD.


  • Frequent respiratory or lung infections

  • Shortness of breath (amplified during exercise)

  • Palpitations, skipped or abnormal heartbeats

  • Swelling of the feet, legs, or abdomen

  • Heart murmur (abnormal sounds that can be heard from a stethoscope)

  • Stroke

Next Steps: Investigation Plan

If your doctor suspects that you have ASD, they may request an  ECG, chest x-ray, transthoracic or transesophageal echocardiogram (TTE, TEE), MRI, and possibly CT scan.

Irregular Heart Rhythms

As a result of the right atrium enlarging because of an ASD, electrical problems (arrhythmias) or disturbances in the heart rhythm can occur. Arrhythmias can range from simple disturbances such as extra beats, or can be more advanced disorders in the form of atrial fibrillation or atrial flutter.

Atrial fibrillation is the chaotic firing of many different areas of the atrial tissue all at once. Atrial fibrillation can require medication to control the heart rate (people who have it may have heart rates between 120-180 beats per minute at rest (normal is 60-100 beats per minute) and may require, under certain circumstances, blood thinning drugs for life. A Holter monitor may help identify a heart rhythm disorder. 

Treatment Options

How do we know if your ASD needs closure?

If the size of the hole on a transesophageal echocardiogram is greater than 10mm it is likely a significant defect. However, the most important factor that determines whether the defect is significant is if it leads to the enlargement of the right atrium and right ventricle.

Transthoracic or Surface Echocardiography (Echo)

A transthoracic echo is a good screening test for many different types of heart diseases. The test looks at heart function, size, and valve function. Often times, in patients with an ASD, the TTE will detect that the right sided chambers are enlarged. This finding is an important step in establishing the diagnosis. Right sided chamber enlargement requires an explanation. About 70 percent of the time an ASD will be visible on the transthoracic echo. If the ASD cannot be seen, your doctor will need to move on to a test that will help sort out the cause of right sided heart enlargement.

Transesophageal Echocardiogram (TEE)

As the TEE probe is passed through the esophagus (similar to the camera used to look at the stomach), your doctor will be able to see the atrial septum of the heart. It offers spectacular views of the atrial chambers. It also is very good at looking at the pulmonary veins. These are the veins that drain from the lung back to the left heart after picking up oxygen. Sometimes one or more of these veins can connect to the right atrium instead of the left. This, in itself can cause the right heart to enlarge. If multiple pulmonary veins connect to the right side of the heart, surgery instead of a closure in catheter laboratory with a device, may be more appropriate. This is a very important thing for your doctor to know.

A TEE can give information on the size of the ASD and whether there is more than one ASD. TEE systematically underestimates the size of ASDs (sometimes by as much as 100%). We say that a 10 mm ASD on TEE is likely significant. We know, however that if the right side of the heart is enlarged and the TEE shows only a 6 mm defect there is one of 2 possibilities:1) the ASD is actually bigger than what we are measuring or 2) there is another cause of right heart enlargement. The TEE is pretty good at figuring this out.

Dr. Eric Horlick on MRI and Echocardiogram

Electrocardiogram (ECG)

The ECG uses electrodes placed on the skin to measure the electrical activity of the heart. It is the best way to identify your heart rhythm and to determine whether any of the heart chambers are enlarged. It may also suggest other issues of importance we may need to deal with at the time of your procedure.

Magnetic Resonance Imaging (MRI)

An MRI of the heart may play an important role in some patients suspected to have an ASD. MRI is the gold standard for measuring the right ventricle. MRI images can be used to calculate a very accurate volume of the right ventricle. In patients with small ASDs this will help us to decide if the ASD needs to be closed. In some patients we cannot find all of the pulmonary veins on TEE. MRI is the best at finding these “missing veins”.

Valve Leakage 

Each ventricular chamber of the heart has a set of 2 associated valves which prevents blood from leaking back into the previous chamber.

As a result of right ventricular enlargement, the ability of the tricuspid valve (valve between right atrium and ventricle) to prevent leakage back into the right atrium is compromised. As the right ventricle enlarges, the tricuspid valve is pulled apart and loses integrity. This is known as tricuspid regurgitation as blood leaks back into the right atrium. This leak causes even more enlargement of the right heart. Once this process starts it becomes a continuous cycle of “more leaking, more right ventricular enlargement, more leaking”, and further reduces the function of the right ventricle.

Dr. Eric Horlick on ASD & Pulmonary Hypertension

Pulmonary Hypertension 

Atrial septal defects may also lead to a condition called pulmonary hypertension (high blood pressure in the lungs).

Due to the increased blood flow to the lungs, the arteries in the lung adapt to protect fragile lung blood vessels. This adaptation may lead to higher pressures in the lung that worsen with age and is directly associated with the size of the ASD. Pulmonary hypertension may worsen the symptoms of exercise intolerance, ie. exacerbated shortness of breath.

As patients with an ASD age, their pulmonary pressure rises and may result in pulmonary hypertension. However, it is very uncommon for young patients, even with large ASDs to develop pulmonary hypertension. This often suggests the presence of another issue besides the ASD.

Shortness of Breath

Up until now we have been discussing the extra flow and volume on the right side of the heart and the changes it causes. It is important to understand that while the right side of the heart is receiving extra blood, the left side is deficient. That is, all of the extra blood that passes from the left atrium to the right atrium actually results in less blood flow getting to the body. This becomes especially problematic during exercise as your muscles are not getting enough nutrients it needs for energy metabolism, and this may be responsible for decreased exercise performance. A clear symptom of this would be exacerbated shortness of breath.

Holter Monitor

A Holter monitor is a small recording device which attaches to leads on the chest. It monitors the heart rhythm continuously for up to 2 weeks. If you complain of palpitations (i.e. extra beats or fast heart beats), your doctor may ask for a Holter prior to the ASD closure procedure.

Treatment Options

Due to variety of the different types of ASDs as well as the range in sizes, and severity, there are a number of different treatment options available.

Dr. Eric Horlick on the ASD Closure Procedure

Transcathater Closure without Surgery

The preferred treatment in 2017 for ASD closure is transcathter closure without surgery. This is a non-surgical approach: only sedation and local anesthesia is used. The procedure is done through a 4 mm diameter catheter that is inserted in the vein in your leg and advanced to the heart.

Following administration of local anesthesia in the skin of your leg and some intravenous sedation to keep you comfortable and relaxed, a cardiac catheter is advanced up to your heart with X ray guidance. The catheter is a thin, flexible tube which is inserted through your groin, and is guided to the location of the ASD in your heart. From a second puncture in the vein in your leg we advance a special miniaturized ultrasound catheter also called ICE (intracardiac echo).  


Once at the ASD site, the cardiologist will use a soft floppy balloon to measure the size of your ASD and will choose an appropriately sized device. Devices range in size from 4 mm to 40 mm. Your doctor will then position the closure device to seal the hole. To ensure quality, and accuracy, the cardiologist will make positional adjustments using ICE. After careful positioning and assessment, the device is released from the catheter and will permanently remain in the defect site, functioning to close the hole. The catheter is then carefully removed, which marks the end of the procedure.

Gore Septal Occluder

The Gore Septal Occluder is an example of an ASD Closure device which is deployed across the hole (defect). This is an effective non-invasive procedure. 

Gore Septal Occluder

ASD Closure Device

What is the Transcatheter ASD Closure?

Your cardiologist will provide full written guidelines in terms of activities and medications. It is important to follow these guidelines, and adhere to the prescriptions. A follow-up appointment will be scheduled 2-3 months post procedure to ensure a safe and smooth recovery. At the follow-up visit you will have an echocardiogram to monitor the device that has been placed and to see post-procedure progress. Your doctor will decide at this time whether a subsequent follow-up should be made at the hospital or with your own family doctor. 

Dr. Eric Horlick on After the ASD Closure Procedure

FAQ: Living with ASD

Living with ASD: Frequently Asked Questions

Does the size of the defect matter?


There is no universal benchmark for the size of the ASD that is considered significant. Generally, holes of sizes 10mm or larger on TEE often require closure. TEE systematically underestimates the size of  an ASD. The gold standard for size is really the size obtained when we measure the ASD using a floppy balloon at the time of the procedure. However, each patient is unique. Your doctor will be able to sort through the information that has been collected and provide you with an opinion. Always ask questions!

Are there any lifestyle restrictions following ASD closure?


In general, there are minimal lifestyle restrictions following ASD closure.  ASD closure is performed to return people to normal functioning and health. Given the procedure is performed through punctures in the blood vessels in the leg, we caution against vigorous exercise in the 2 weeks following the procedure. The wounds need to completely heal before any form of forceful exercise is performed.

Does the device ever need to be changed?


No, the device is a permanent implant. Once implanted, the heart will grow over it and cover it almost entirely.

Will I need any further treatments post-procedure?


In the short term following your procedure, you will be given a follow up appointment to monitor your progress. You will see the doctor and an echocardiogram will be performed. If all is well your doctor will send you back to your local physician. If there are any unresolved issues or questions your doctor may elect to have you follow up at the hospital again. 


Can I play sports?

You may return back to your normal physical activities after 14 days or so . You should start off with walking at a normal pace and gradually begin increasing aerobic exercise intensity after the second week. Contact sports should be avoided for at least a month after surgery.


Will my heart go back to normal following ASD closure?

Patients under the age of 40 at time of closure should expect their heart to return to normal. A significant reduction in cardiac chamber size is observed in this age group. For patients over 40, there is a possibility that the heart may not regain its normal state.


Will OHIP (public insurance) cover my ASD closure?


Yes, ASD closure is completely covered by OHIP.


How urgent is the treatment?

The urgency of treatment is highly case dependent. It is rare for an ASD closure to be truly urgent. In most cases there is no urgent need to repair the hole. If treatment is required, the urgency depends on the type, location, and size of the hole, in addition to signs of atrial enlargement. Usually a delay of several months is not significant. It is more important to thoroughly assess the problem than to jump in and perform a procedure urgently.


Why was my ASD only diagnosed as an adult, despite such advances in healthcare?

They physical signs of an ASD are very subtle, often escaping experienced physicians, the symptoms are vague and may commonly attributed to other factors. Exercise intolerance may be attributed to being “out of shape”. Our program has seen almost 2000 patients with ASDs, none were diagnosed with a stethoscope alone.

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Questions specific to your appointment? Call Sue!

Socorro (Sue) Jimeno

Clinical Coordinator, Structural Heart Disease Program 

Phone: 416 340 4800, extension 6258

Fax: 416 340 4741


Questions? Call our Office!

Structural Heart Disease Program (Patients)

Socorro (Sue) Jimeno, Clinical Coordinator

Phone: 416-340-4800, extension 6258

Fax: 416-340-4741

Referrals & Administrative Issues:

Toronto General Hospital 

200 Elizabeth Street | 6E - 249

Toronto, Ontario M5G 2C4

Phone: 416-340-3835

Fax: 416-340-3000

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