Pediartic cardioloist in yelahanka A ventricular septal defect (VSD) is a hole in the heart that's present at birth (congenital heart defect). The hole is between the lower heart chambers (right and left ventricles). It allows oxygen-rich blood to move back into the lungs instead of being pumped to the rest of the body Large (6-10 mm in diameter) These VSDs often require surgery (the timing of the surgery can vary slightly). Repair of a large VSD before age 2 can prevent damage to the heart and lungs