What Are the Risks of an Untreated Atrial Septal Defect?

If you choose not to treat an atrial septal defect (ASD), the heart is forced to pump extra blood over a period of years or decades. It is important to know that these long-term risks apply primarily to moderate or large ASDs that cause right heart enlargement. A tiny, incidental hole may never cause issues.

For many people with a significant ASD, there are no noticeable symptoms during childhood or early adulthood. However, over time, the constant extra workload on the right side of the heart can lead to structural changes, irregular heartbeats, high blood pressure in the lungs, and stroke ^[1][2]. While an untreated, large ASD can reduce life expectancy, timely closure can halt this damage and often restore your long-term health ^[3][4].

The Domino Effect on the Heart

An ASD allows oxygen-rich blood to flow from the left atrium into the right atrium, which is called a left-to-right shunt. Think of it like a leaky valve in a plumbing system: the right side of your heart and your lungs receive more fluid than they were designed to handle. The progressive long-term risks usually follow a cascade of changes:

1. Right Heart Volume Overload

Because of the extra blood crossing through the hole, the right side of the heart has to work much harder. Over years, this constant “volume overload” causes the right atrium and the right ventricle to stretch and enlarge (dilate) ^[1][4]. Eventually, the stretched heart muscle can lose its ability to pump efficiently, potentially leading to right-sided heart failure ^[4][5]. Symptoms of heart failure include fatigue, shortness of breath, and swelling in the legs or abdomen.

Note: If you are beginning to experience new symptoms like shortness of breath during exercise, this is a major warning sign that the cascade of heart changes is already underway. It is critical to discuss these symptoms with your cardiologist promptly.

2. Atrial Fibrillation and Arrhythmias

As the upper chambers (the atria) of the heart stretch due to the extra blood volume, their electrical systems can become disrupted. This places adults with an untreated ASD at a high risk of developing arrhythmias (irregular heart rhythms), most commonly atrial fibrillation (AF) or atrial flutter ^[6][7]. The risk of developing these arrhythmias increases significantly as you get older, especially after age 40 ^[8]. Atrial fibrillation can increase the risk of blood clots forming in the heart ^[9].

3. Paradoxical Embolism and Stroke

Even without atrial fibrillation, an ASD presents a unique stroke risk. Normally, if a small blood clot forms in the veins of your legs, it travels to the lungs where it is safely filtered out. However, if you have an ASD, a clot can cross directly through the hole from the right side of the heart to the left side ^[2][10]. This is called a paradoxical embolism. Once on the left side, the clot can be pumped to the brain, causing a stroke ^[11]. This risk is a major reason why doctors may recommend closing an ASD even in younger, asymptomatic patients.

4. Pulmonary Hypertension

The extra blood flowing into the right side of the heart gets pumped directly into the lungs. Over many years, this increased blood flow can cause the blood vessels in the lungs to become stiff and narrow. This condition is known as pulmonary arterial hypertension (PAH), which is high blood pressure specifically in the lungs ^[12][13]. PAH forces the right ventricle to pump even harder to push blood through the narrowed vessels, accelerating heart damage.

5. Eisenmenger Syndrome

In rare cases, if a large ASD is left untreated for decades, the pulmonary hypertension can become so severe that the pressure in the right side of the heart exceeds the pressure in the left side. When this happens, the blood flow through the ASD reverses—flowing from right to left ^[14][15]. This means oxygen-poor blood is pumped out to the rest of the body. This condition is called Eisenmenger syndrome. It causes cyanosis (a bluish tint to the skin and lips due to low oxygen levels) and is a very serious, life-threatening complication ^[14][15]. Once Eisenmenger syndrome develops, the damage to the lungs is permanent, and the ASD can no longer be safely closed ^[16].

Life Expectancy and Moving Forward

Historical data on people with untreated ASDs show that while many live normal lives into their twenties and thirties, the toll on the heart often becomes apparent later. Mortality rates in untreated individuals become significantly more common after the age of 40 (rising from less than 1% per year in youth to higher single-digit percentages later in life) ^[3].

However, it’s important to remember that these statistics reflect what happens without modern treatment. Today, ASD closure procedures are often minimally invasive (using a catheter rather than open-heart surgery), highly successful, and require only a short hospital stay ^[17][18]. Timely closure can completely halt this domino effect, reversing right heart enlargement and protecting your long-term health ^[4][19]. Until a decision is made, regular echocardiograms and check-ups with an adult congenital cardiologist are essential to monitor your heart’s size and function.