Pathophysiology
At birth, closure of the septum is necessary to allow the heart to develop its four chambers, separating the blood that goes into the lungs for re-oxygenation, from the blood that is oxygen-rich traveling from the lungs into the left heart to be pumped out into the body. Insufficient closure of the intraventricular septum is named VSD. Lack of closure between the two atria is called Atrial Septal Defect, (ASD)

The lack of closure may occur in different positions and in different size.