An atrial septal defect (ASD) — sometimes referred to as a hole in the heart — is a type of congenital heart defect in which there is an abnormal opening in the dividing wall between the upper filling chambers of the heart (the atria).

The heart has four chambers: The two lower pumping chambers are called the ventricles, and the two upper filling chambers are the atria.

In a healthy heart, blood that returns from the body to the right-sided filling chamber (right atrium) is low in oxygen. This blood passes to the right-sided pumping chamber (right ventricle), and then to the lungs to receive oxygen. The blood that has been enriched with oxygen returns to the left atrium, and then to the left ventricle. It's then pumped out to the body through the aorta, a large blood vessel that carries the blood to the smaller blood vessels in the body. The right and left filling chambers are separated by a thin shared wall, called the atrial septum.

Kids with an atrial septal defect have an opening in the wall (septum) between the atria. As a result, some oxygenated blood from the left atrium flows through the hole in the septum into the right atrium, where it mixes with oxygen-poor blood and increases the total amount of blood that flows toward the lungs. The increased blood flow to the lungs creates creates a swishing sound, known as a heart murmur. This heart murmur, along with other specific heart sounds that can be detected by a cardiologist, can be clues that a child has an ASD.

ASDs can be located in different places on the atrial septum, and they can be different sizes. The symptoms and medical treatment of the defect will depend on those factors. In some rare cases, ASDs are part of more complex types of congenital heart disease. It's not clear why, but ASDs are more common in girls than in boys.

Causes

ASDs occur during fatal development of the heart and are present at birth. During the first weeks after conception, the heart develops. If a problem occurs during this process, a hole in the atrial septum may result.

In some cases, the tendency to develop a ASD might be genetic. Genetic syndromes can cause extra or missing pieces of chromosomes that can be associated with ASD. For the vast majority of children with a defect, however, there's no clear cause.

Signs and Symptoms

The size of an ASD and its location in the heart will determine what kinds of symptoms a child experiences. Most kids who have ASDs seem healthy and appear to have no symptoms. Generally, they feel well and grow and gain weight normally.
Children with larger, more severe ASDs, however, might have some of these signs or symptoms:

• Poor appetite
  
• Poor growth
  
• Fatigue
  
• Shortness of breath
  
• Lung problems and infections, such as pneumonia

If an ASD is not treated, health complications can develop later, including an abnormal heart rhythm (known as an atrial arrhythmia) and problems with how well the heart pumps blood. As kids with ASDs get older, they also might be at an increased risk for stroke, since a blood clot that develops can pass through the hole in the wall between the atria and travel to the brain. Pulmonary hypertension (high blood pressure in the lungs) also can develop over time in older patients with larger untreated ASDs.