The Septum--The wall dividing the right side of the heart from the left side.
Atrial septal defect
(ASD) is a form of congenital heart defect that enables blood flow between the left and right atria via the interatrial septum
A ventricular septal defect
(VSD) is a defect in the ventricular septum, the wall dividing the left and right ventricles of the heart.