Pathophysiology: In atrial septal defect, left and right atrial pressures usually are equal; thus, no pressure gradient exists between the atria. However, the increased thickness of the left ventricle as compared to the right ventricle makes the left ventricle less compliant and, therefore, harder to fill. Blood flow takes the path of least resistance and, thus, is shunted from the left atrium to the right atrium. The net effect is to increase the volume work of the right ventricle. The increased volume pumped through the pulmonary vasculature may lead to architectural changes in the pulmonary vasculature and to the development of irreversible pulmonary hypertension - a serious but rare complication.

Atrial Septal Defect (ASD) is a congenital heart disease that allows blood to flow from the left atrium into the right atrium, and occasionally from the right atrium to the left atrium. This defect creates what is called shunting, or mixing of the oxygenated blood, from the left side of the heart with the deoxygenated blood of the right side. Such defects in the atrial septum account for 12% of all congenital heart diseases and are more common in women. Aside from incomplete closure of the foramen ovale, septal defect occurs during the development of the fetal heart in the first two weeks after conception. Although there are some suggestions that some forms may be genetic, the cause of most ASDs is unknown.

A septal defect is a hole in the septum, the muscle wall separating the heart's upper-right chamber (the right atrium) from the upper-left chamber (the left atrium) and the lower-right chamber (the right ventricle) from the lower-left chamber (the left ventricle). A septal defect is sometimes called "a hole in the heart

Atrial septal defect (ASD) means that the hole is located between the upper chambers of the heart (the right and left atria). Since the pressure is higher on the left side of the heart, blood gets pushed through the hole from left to right. This may cause the right atrium to become enlarged.

Blue Baby Syndrome

Cyanotic heart problems, commonly known as Blue Baby Syndrome, can occur as a consequence of a right to left shunt. The deoxygenated (blue) blood will bypass the lungs and circulate throughout the systemic circulation resulting in blue coloration of the skin (right photo). Blue baby syndrome accounts for 25% of congenital heart defects. Although atrial septal defects can occasionally cause this defect, the most common cause of the disease is tetrology of fallot.