A VSD lets blood from the left ventricle (where it is under relatively high pressure) shunt into the right ventricle which has to do extra work to handle the additional blood, may have trouble keeping up with the load, enlarge, and fail. The lungs receive too much blood under too great pressure, the arterioles (small arteries) in the lungs thicken up in response, and permanent vascular damage can be done to the lungs.
Small VSDs (less than 0.5 square cm in area) permit only minimal shunting of blood and the pressure in the right ventricle remains normal and the heart (and lungs) function normally. Surgical repair is not recommended for small VSDs.
No matter what size a VSD is, it carries an increased risk for infection of the heart walls and valves (endocarditis). To prevent endocarditis, anyone with a VSD should take antibiotics before dental and other particular procedures.
With a large VSD (usually one greater than 1.0 square cm in area), there is a significant shunt into the right ventricle, excessive blood flow into the lungs, and pulmonary hypertension. The child may have labored breathing, difficulty feeding, and grow poorly. Medically, the heart that has a large VSD should be kept strong. Vascular disease in the lungs must not be allowed to develop. Surgery should be done to close a large VSD.
The prognosis (outlook) with VSD is generally excellent.