Atrial Septal Defect


An atrial septal defect (ASD) is a hole in the atrial septum – the muscular wall that separates the heart’s two upper chambers, or atria. This defect makes your heart work harder than it should. ASD develops before birth, meaning it’s a congenital defect.

Because of the hole in the atrial septum, oxygen-rich blood from the left chamber mixes with oxygen-poor blood from the right chamber. This means some oxygen-rich blood is pumped to your lungs – where it has just been – instead of to your body. 

ASDs can be small, medium or large. If the hole is small, it may repair itself during childhood. They can occur in the lower, middle or upper parts of the atrial septum. Holes in the middle part of the septum are the most common, affecting about 80% of those born with this condition. Holes in the lower and upper parts of the atrial septum are very rare.


The most common symptom of an atrial septal defect is a heart murmur. This is an extra or unusual sound during a heartbeat. Other ASD symptoms include:

  • Arrhythmia
  • Pulmonary hypertension 
  • Right heart failure
  • Stroke
Symptoms of ASD typically appear in people age 30 and older. Most infants born with ASD have no symptoms, even when the hole is large. Often, if the hole is smaller, it closes as the heart grows, so there are no symptoms or complications.


Doctors often don’t diagnose ASD until later in childhood or in adulthood. If an ASD is suspected, your doctor may perform additional cardiac tests. These include:

Services & Treatment

Children and adults who don’t have symptoms don’t need treatment. If treatment is necessary, most ASDs are treated with cardiac catheterization. In rare cases, surgery is performed.

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