An atrial septal defect (ASD) is a hole in the wall that separates the two upper chambers of the heart. About 13 out of every 10,000 babies in the United States are born with one. Some ASDs are small and never cause problems, while larger ones allow blood to flow abnormally between the chambers, forcing the heart and lungs to work harder over time. It is one of the most common congenital heart defects, and many people don’t learn they have one until adulthood.
How the Defect Works
Your heart has four chambers. The two upper ones, the atria, are separated by a thin wall called the atrial septum. Normally this wall keeps oxygen-rich blood on the left side from mixing with oxygen-poor blood on the right. When there’s a hole in the septum, blood from the left atrium leaks into the right atrium with each heartbeat. Because pressure is higher on the left side, the flow almost always goes left to right.
This extra blood gets pumped to the lungs unnecessarily. A small hole sends a trivial amount and may never matter. A large one floods the right side of the heart and the lung arteries with excess blood, gradually stretching and weakening the right chambers. Over years or decades, this overload can raise blood pressure in the lungs and lead to serious complications.
Types of Atrial Septal Defects
Not all ASDs are in the same spot, and the location matters for treatment decisions.
- Secundum ASD: The most common type, located in the middle of the septum at a structure called the fossa ovalis. This is the type most likely to be treatable without open-heart surgery.
- Primum ASD: Sits near the bottom of the septum, close to the heart’s valves. It falls within a broader group of defects that can also involve the valves between the upper and lower chambers.
- Sinus venosus defect: Found near the top of the septum where a major vein enters the right atrium. It is almost always accompanied by at least one pulmonary vein draining into the wrong chamber.
- Coronary sinus defect: The rarest type. A gap between the coronary sinus (a small vein channel on the back of the heart) and the left atrium creates an indirect path for blood to shunt from left to right.
Causes and Risk Factors
ASDs form during the first weeks of fetal development when the wall between the atria doesn’t close completely. In most cases, no single cause is identified. The defect is sometimes linked to genetic syndromes, including Down syndrome and Holt-Oram syndrome, a condition that also affects the bones of the hands and arms. Certain maternal factors during pregnancy, such as rubella infection, poorly controlled diabetes, and alcohol or drug exposure, have been associated with a higher risk of congenital heart defects generally, though pinpointing the exact trigger for any individual case is rarely possible.
Symptoms in Children and Adults
Small ASDs often produce no symptoms at all. A child may grow, play, and hit every milestone normally. The only clue might be a heart murmur picked up during a routine exam. Many small defects close on their own during the first few years of life.
Larger defects tell a different story, though even these can stay silent for years. Children with significant ASDs may tire more easily, grow more slowly, or get frequent respiratory infections. Adults who weren’t diagnosed as children often begin noticing symptoms in their 30s or 40s as the heart’s right side gradually enlarges. Common complaints include shortness of breath during exercise, fatigue that seems disproportionate to activity level, swelling in the legs or feet, and heart palpitations caused by irregular rhythms.
An irregular heart rhythm called atrial fibrillation becomes increasingly common in adults with unrepaired ASDs, particularly after age 40. The stretched right atrium creates the electrical conditions for this rhythm disturbance, which itself raises stroke risk.
Complications of an Untreated ASD
Left unrepaired, a significant ASD increases the risk of several serious problems over a lifetime: atrial fibrillation, stroke, heart failure, and pulmonary hypertension (high blood pressure in the lung arteries). These risks climb with age.
Pulmonary hypertension develops because the lung arteries receive more blood flow than they were designed to handle, year after year. The artery walls thicken and stiffen in response. In rare cases, this progresses to a condition called Eisenmenger syndrome, where lung pressure rises so high that blood flow across the hole actually reverses direction, sending oxygen-poor blood into the body. At that stage, closing the defect is no longer safe because the right side of the heart has come to depend on the hole as a pressure relief valve. Eisenmenger syndrome typically takes many years to develop and is most associated with large, long-standing defects.
Stroke can also occur through a mechanism called paradoxical embolism. Normally, a small blood clot that forms in a vein would travel to the lungs and be filtered out. With a hole in the septum, that clot can cross from the right atrium to the left and travel to the brain instead.
How ASDs Are Diagnosed
Diagnosis typically starts with a physical exam that reveals a heart murmur, followed by an echocardiogram, the primary tool for confirming an ASD. This ultrasound of the heart shows the location and size of the hole, how much extra blood is flowing through it, and whether the right side of the heart has started to enlarge from the added volume.
A standard echocardiogram done through the chest wall works well for most cases, especially in children. When the image isn’t clear enough, or when the defect’s exact edges need to be mapped before a procedure, a transesophageal echocardiogram provides a closer, more detailed view by placing a small ultrasound probe in the esophagus, just behind the heart. An electrocardiogram (ECG) and chest X-ray often provide supporting clues, such as signs of right heart enlargement or increased blood flow to the lungs.
Treatment Options
Not every ASD needs to be closed. Small defects that don’t cause the right side of the heart to enlarge are often just monitored over time. Closure is recommended when the defect is sending enough extra blood to the lungs to cause measurable changes in the heart’s size or function.
Catheter-Based Closure
For secundum ASDs, the most common approach is transcatheter closure. A thin tube is threaded through a vein in the groin up to the heart, and a small device is positioned across the hole, sealing it from both sides. This works for defects up to about 35 mm in diameter, provided there is enough surrounding tissue (called “rims”) to anchor the device securely. The procedure is done under sedation or general anesthesia, and most people resume normal activity within about a week.
Surgical Repair
Primum ASDs, sinus venosus defects, and coronary sinus defects generally require open-heart surgery because their location or associated abnormalities make catheter devices impractical. During surgery, the hole is closed with stitches or a patch. Recovery from surgical repair takes longer, with physical activity typically limited for a few weeks.
After either type of closure, you’ll likely take blood-thinning medication for about six months to prevent clots from forming on the closure device or repair site while the heart tissue heals over it.
Life After ASD Closure
When an ASD is closed in childhood or early adulthood before complications develop, the outlook is excellent. The right side of the heart often returns to a normal size within months, and most people go on to live without restrictions. Closure later in life still provides significant benefit, reducing the risk of stroke and heart failure progression, though some changes like atrial fibrillation may persist if the heart’s rhythm was already affected before repair.
People who had an ASD closed will need periodic follow-up with a cardiologist, typically with an echocardiogram every few years, to ensure the closure remains intact and the heart is functioning well. For those whose defect was repaired early and completely, long-term activity restrictions are rare, and most can exercise, work, and go through pregnancy without added risk.