A ventricular septal defect (VSD) is a defect in a part of the septum, the tissue that separates the two ventricles of the heart, and is a type of congenital heart disease. It can be understood as a “hole” in the heart that is not growing properly. When the defect is large, the heart needs to increase the contraction of the heart muscle to pump enough oxygenated blood throughout the body. When the defect is small, the patient can usually feel no discomfort. Sometimes children with ventricular septal defects are combined with other heart abnormalities.