A ventricular septal defect ( VSD ) is a defect in the ventricular
septum, the wall dividing the left and right ventricles of the heart. The
extent of the opening may vary from pin size to complete absence of the
ventricular septum, creating one common ventricle. The ventricular septum
consists of an inferior muscular and superior membranous portion and is
extensively innervated with conducting cardiomyocytes.
The membranous portion, which is close to the atrioventricular node, is most
commonly affected in adults and older children in the United States. It is
also the type that will most commonly require surgical intervention,
comprising over 80% of cases.