Atrial septal defect is an abnormality of the upper chambers of the heart (atria) where the wall between the right and left atria does not close completely. This defect is present at birth (congenital).

Atrial septal defect (ASD) is a congenital heart defect. In fetal circulation, there is normally an opening between the two atria (the upper chambers of the heart) to allow blood to bypass the lungs. This opening usually closes around the time the baby is born. If the ASD is persistent, blood continues to flow from the left to the right atria. This is called a shunt. Sometimes, blood flows from the right atrium to the left atrium (a right to left shunt).

ASD is not very common. When the person has no other congenital defect, symptoms may be absent, particularly in children. Symptoms may begin any time after birth through childhood. Individuals with ASD are at an increased risk for developing a number of complications including:

• Pulmonary overcirculation
• Heart failure
• Atrial fibrillation (in adults)
• Stroke
• Pulmonary hypertension

• Frequent respiratory infections in children
• Difficulty breathing (dyspnea)
• Shortness of breath with activity
• Sensation of feeling the heart beat (palpitations) in adults

Note: People with small-to-moderate-sized defects may show no symptoms, or not until middle age or later.

Rarely, there may be a palpable pulsation of the pulmonary artery in the chest. Examination with a stethoscope (auscultation) of the heart usually reveals abnormal heart sounds. There may be a murmur caused by the increased blood flow across the pulmonic valve, and the second heart sound is widely split and fixed. Signs of heart failure can occur in adults.

If the shunt is large, increased blood flow across the tricuspid valve (between the right atrium and ventricle) may be responsible for an additional murmur when the heart relaxes between beats.

Tests that may be performed in the diagnosis of ASD include:

• Chest x-ray
• Echocardiography (ultrasound of the heart)
• Doppler study of the heart
• Transesophageal echocardiography (TEE)
• Cardiac catheterization
• Coronary angiography (for patients over 35 years old)
• MRI of heart
• ECG - may show atrial fibrillation in adults, right atrial and ventricular enlargement, or a pattern of delayed electrical conduction in the heart.