Ventricular septal defect (VSD) is the most common form of congenital cardiovascular anomaly, occurring in nearly 50% of all infants with a congenital heart defect and accounting for 14 to 16% of cardiac defects that require invasive treatment within the first year of life. Congenital VSDs may occur alone or in combination with other cardiac malformations. Large VSDs that go unrepaired may give rise to cardiac enlargement, congestive heart failure, pulmonary hypertension, Eisenmenger's syndrome, delayed fetal brain development, arrhythmias, and even sudden cardiac death. [From OMIM]