According to the American Heart Assocation, an ASD is an opening or hole (defect) in the wall (septum) that separates the top two chambers of the heart (atria). This defect allows oxygen-rich blood to leak into the oxygen-poor blood chambers in the heart. ASD is a defect in the septum between the heart’s two upper chambers. The septum is a wall that separates the heart’s left and right sides.
Every child is born with an opening between the upper heart chambers. It’s a normal fetal opening that allows blood to detour away from the lungs before birth. After birth, the opening is no longer needed and usually closes or becomes very small within several weeks or months. Sometimes the opening is larger than normal and doesn’t close after birth. In most children the cause isn’t known. Some children can have other heart defects along with ASD.
Children with an ASD often have no symptoms. If the opening is small, it won’t cause symptoms because the heart and lungs don’t have to work harder. If the opening is large, the only abnormal finding may be a murmur (noise heard with a stethoscope) and other abnormal heart sounds. In children with a large ASD, the main risk is to the blood vessels in the lungs because more blood than normal is being pumped there. Over time, usually many years, this may cause permanent damage to the lung blood vessels. If the ASD is large, it can be closed with open heart surgery or a catheterization procedure.