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What is atrial septal defect?

Atrial septal defect (ASD) is a common structural heart defect that can be present at birth (congenital). It is a hole in the septum (wall) that separates the two upper chambers (atria) of the heart. The defect causes oxygenated blood to leak from the heart’s left side into the right side, which the heart then pumps back to the lungs, working harder than normal. Extra blood in the lung arteries also can damage the tissue, and make the person more at risk for pneumonia and bronchitis.


There often are no symptoms, especially if the hole is small. In adults, symptoms of ASD often begin by age 30 but in some cases may not occur until much later. ASD symptoms may include:

  • Heart murmur, a whooshing sound that can be heard through a stethoscope
  • Shortness of breath, especially when exercising
  • Fatigue
  • Swelling of legs, feet or abdomen
  • Heart palpitations or skipped beats
  • Frequent lung infections
  • Stroke
  • Bluish skin color
  • Heart failure

Sometimes an ASD is diagnosed only later in life because the heart’s ability to pump has been compromised.


The cause of ASD is unknown, but it’s possible that genetics is involved.


The condition sometimes is discovered during a regular doctor’s visit when the doctor notices the presence of a cardiac murmur or abnormal heart sounds through the stethoscope.