Perimembranous VSD is the commonest type of VSD. VSD stands for ventricular septal defect, a hole in the wall between the lower chambers of the heart. When there is a ventricular septal defect, blood shunts from the left ventricle to the right ventricle. Left ventricle is the lower left chamber and right ventricle the lower right chamber. This leads to increased blood flow to the lungs. VSD usually occurs as a birth defect, though it can rarely occur in the adult after a heart attack. If the VSD is very large, excessive blood flow to the lungs, which returns to the left ventricle later can sometimes lead to heart failure.