Table 4.15 - Types of Ventricular Septal Defects.

Membranous septal defect - incomplete closure of the interventricular foramen and failure of the membranous septum to develop; the most common.
Muscular septal defect - ("Swiss cheese" defect) may result formation of muscular septum.
Absence of interventricular septum - complete failure of septum to develop; results in 3-chambered heart (cortriloculare biatriatum).