What is a Atrial Spetal Defect ( ASD)? An opening or hole (defect) in the wall (septum) that separates the upper two chambers of the heart i.e the right and left atria . As a result of which the oxygenated blood coming from the lungs into the left upper chamber (left Atria) atria passes through this defect in to the right upper chamber (right Atria) and mixes with the impure blood coming from the whole body and entering the right upper chamber. What are the causes of ASD in c