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 about 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.

ASD is present in 4 out of 100,000 people. When the person has no other congenital defect, symptoms may be absent, particularly in children. Symptoms usually have manifested by age 30. Individuals with ASD are at an increased risk for developing a number of complications including:

• Infective endocarditis
• Heart failure
• Atrial fibrillation
• Stroke

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

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 signs of heart failure. 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.

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 chest
• ECG  - may show atrial fibrillation, right atrial enlargement, or a pattern of delayed electrical conduction in the heart.