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Atrial septal defect (ASD) is a congenital heart defect in which the wall that separates the upper heart chambers (atria) does not close completely. Congenital means the defect is present at birth.
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. If too much blood moves to the right side of the heart, pressures in the lungs build up. The shunt can be reversed so that blood flows from right to left. Small atrial septal defects often cause very few problems and may be found much later in life. Many problems can occur if the shunt is large, however. In advanced and severe cases with large shunts the increased pressure on the right side of the heart would result in reversal of blood flow (now from right to left). This usually results in significant shortness of breath.
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:
Webb GD, Smallhorn JF, Therrien J, et al. Congenital heart disease. Zipes DP, Libby P, Bonow RO, Braunwald E, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 8th ed. St. Louis, Mo: WB Saunders; 2007:chap 61.
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