Two of the more common congenital disorders are ventricular septal defects and atrial septal defects, or VSD and ASD, respectively. A VSD is a hole that occurs in the septum, or wall, that lies between the left and right ventricles, or lower chambers. An ASD is a hole that occurs in the septum between the left and right atria, or upper chambers. In both cases, oxygen-rich blood from the left side seeps into the right side. This decreases the amount of circulating oxygen and puts additional strain on the heart and lungs.