A normal heart has a muscular wall known as the atrial septum that separates the organ’s upper chambers, or the left and right atria. If there is a defect in this wall, it’s known as an atrial septal defect.

In a normal newborn’s heart, the heart’s left chambers pump oxygenated blood to the body, while the right chambers pump unoxygenated blood to the lungs. An atrial septal defect allows blood to travel from the left side of the heart to the right side (because the pressure in the left side is higher), and then into the lungs instead to the body. This puts stress on the heart and causes health problems.

The most common type of atrial septal defect is known as a patent foramen ovale. The foramen ovale is a natural hole in a newborn’s atrial septum that closes immediately after birth. This hole allows blood to bypass the lungs during development.

Atrial septal defects range in size. Generally, small defects don’t affect the heart’s function, cause symptoms, or need treatment. In fact, many small atrial septal defects close on their own. Medium and large atrial septal defects are more likely to leak significant blood from one atrium to the other. They are also more likely to require treatment and usually do not close on their own.

There are three major atrial septal defect types. The most common atrial septal defect, the secundum, is in the middle of the atrial septum. This defect type affects about eight in 10 babies born with atrial septal defect. Primum defects affect the lower part of the atrial septum. Primum defects don’t heal on their own and often are associated with heart valve problems. Sinus venosus defects occur in the upper atrial septum. They also don’t close on their own.

Large atrial septal defects might cause a heart murmur, which physicians hear through their stethoscopes as an abnormal sound in the heartbeat. Other symptoms that can begin after birth through childhood include breathing difficulty, frequent respiratory infections, and shortness of breath with activity.

Physicians can diagnose atrial septal defect with a clinical exam (by listening for a murmur) and an echocardiogram. If that’s inconclusive, other tests might be necessary.

Effective treatments for children with large atrial septal defects include closing the hole by way of cardiac catheterization or, in more complex cases, fixing it with open heart surgery. Even when they don’t have many symptoms, children might be treated to prevent heart problems that can occur decades later. Long-term complications from atrial septal defect include right heart failure, arrhythmias (or irregular heartbeats), stroke, or pulmonary hypertension (increased pulmonary artery pressure). These can be prevented with early treatment.

The long-term outlook for children with this congenital heart defect is excellent. Even those who have surgery or catheterization to correct the deformity can usually resume a normal life after healing from the procedure.


  • An atrial septal defect is a hole in the septum separating the newborn’s left and right atria.
  • Small defects usually don’t need treatment and may heal on their own.
  • Larger defects can cause heart problems—especially into adulthood—and should be treated.

Last reviewed by Sara Connolly, MD. Review Date: August 2019


  1. Centers for Disease Control and Prevention (CDC). Facts about Atrial Septal Defect.
  2. American Heart Association. Atrial Septal Defect.


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