Ventricular septal defects are the most common of all congenital cardiac malformations. In 50% of cases VSD occurs as an isolated defect and in the remaining 50% it is part of a more complex malformation. Incidence
of isolated VSD has been reported to be 10 to 12 per 10,000 live births. Ventricular septal defects are found most frequently in the membranous part of the septum (membranous VSD). However, much less commonly, the muscular part of the septum may have a defect, constituting a muscular VSD. Small ventricular septal defects allow some shunting of blood but are of little clinical significance. Large defects allow large volumes of blood to shunt from the left to the right ventricle. This causes enlargement of the right ventricle and produces pulmonary hypertension due to excessive blood flow into the pulmonary artery. Clinical features include dyspnea (difficulty in breathing) and cardiac failure early in infancy. Large VSDs shorten life if surgery is not performed.