An inherited defect of the HEART. The septum (partition) separating the two ventricles is pierced by a hole which, if large, results in blood being diverted to the LUNGS at a greater pressure than normal. Half of the defects seal themselves spontaneously, but where spontaneous closure is considered unlikely, early surgical correction (repair of the septal defect) avoids the most serious complication – irreversible PULMONARY HYPERTENSION. A quarter of patients with VSD have other cardiac defects.