The most common interventricular septal defect (VSD) seen clinically is

B. The most common of all cardiac congenital malformations seen clinically are membra-nous VSDs. The membranous interventricular septum forms by the proliferation and fusion of tissue from three different sources: the right and left bulbar ridges and the atrioventricular (AV) cushions. Because of this complex formation, the probability of defects is very high.