Atrial septal defect, ASD, is a congenital defect of the heart, or one present at birth. There is an abnormal opening in the wall that separates the two upper chambers of the heart.
The heart has four chambers. The two upper chambers are called the atria. An ASD is a defect or hole in the wall between these chambers. The hole allows blood to flow abnormally between the chambers. ASD is a fairly common cause of congenital heart disease.
The exact cause of ASD is often unknown. The heart develops abnormally before the person is born. Some factors that increase the risk of ASD are: