Ventricular septal defect, or VSD, is a hole in the septum that separates the right and left ventricles of the heart. This defect causes blood from the higher pressure left ventricle to be pushed into the right ventricle of the heart. If the defect is large, there will be abnormally high blood pressures in the right ventricle and the pulmonary arteries. When required, VSDs can be surgically closed with a patch. This restores normal ventricular blood flow.