Congenital heart defects (also called congenital heart diseases) are structural abnormalities that are present in the heart at birth.

What is an atrial septal defect?

An atrial septal defect (ASD) is a hole in the septum, or muscular wall, that separates the heart’s two upper chambers (atria). An ASD occurs when part of the atrial septum does not form properly.

Within the broad category of ASDs, there are several types of defects. Atrial septal defects are classified by where they occur and their size. A secundum ASD is a hole in the middle of the atrial septum, which lets blood flow from the left chamber to the right chamber, or from the right chamber to the left chamber, depending on pressures in the atria.

A patent foraman ovale (PFO) is a "flap" that is present when the atrial septum does not close properly at birth. A PFO allows blood to flow from the right atrium to the left atrium. This type of defect generally only permits blood flow when there is more pressure inside the chest, such as straining during a bowel movement, coughing or sneezing. Learn more about PFO.

More complicated and rare types of ASDs involve different parts of the septum and also involve abnormal blood return from the lungs (sinus venosus) or heart valve abnormalities (primum ASDs).

What causes ASDs?

About 10 percent of congenital heart problems are caused by specific genetic defects. Most congenital heart defects are likely due to maternal environmental factors combined with a genetic predisposition. Environmental factors include use of alcohol and street drugs, as well as diseases such as diabetes, lupus and rubella

Who is affected by ASDs?

Atrial septal defects account for about seven percent of all congenital heart defects, making them the third most common type. In addition, ASDs are the most common congenital defect in adults and are more common among women than men.

What are the long-term effects of ASDs?

Normally, the right side of the heart pumps blood that is low in oxygen to the lungs, while the heart’s left side pumps oxygen-rich blood to the body. When there is an ASD, blood from the left and right sides mix, and the heart generally does not work at its most efficient level. The risk of problems is greater when the defect is large (greater than 2 cm). Problems may include:

• Right heart enlargement (leading to right heart failure)

• Heart rhythm disturbances, including atrial fibrillation or atrial flutter, occur in 50 to 60 percent of all patients over age 40 with an ASD.

• Stroke

• Pulmonary hypertension (high blood pressure in the arteries that supply blood to the lungs). Blood normally flows from the left side of the heart to the right, but in patients with an ASD and severe pulmonary hypertension, the blood flow across the ASD can reverse (flow right to left). As a result, oxygen levels in the blood will decrease, leading to a condition known as Eisenmenger syndrome.

• Leaking tricuspid and mitral valves as a result of enlargement of the heart

What are the symptoms of ASDs?

Although ASDs are present from birth, there are usually no associated symptoms, and the condition can go undetected until adulthood. In some patients, the defect is discovered incidentally during a chest X-ray that reveals enlargement of the right side of the heart. By age 50, an individual with an ASD may start having symptoms such as shortness of breath, fainting, irregular heart rhythms or fatigue after mild activity or exercise.