Ventricular-Septal Defect (VSD). The most common congenital heart defect. It is often associated with other defects like the tetralogy of Fallot, transposition of the great arteries, and atrial-septal defects. This is an acyanotic defect in which the ventricular septum does not fuse, and oxygenated blood from the left ventrical gets pumped back through the shunt into the right. After time, the extra work required of the right ventricle may reverse the shunt and make it cyanotic.