Over the course of time, new developments associated with embryogenesis of the murine heart have served to clarify the developmental processes observed in the human heart. This evidence allows for creation of a developmental framework for many congenital cardiac defects. Here, we aim to solidify the framework related to the categorization of both solitary and multiple ventricular septal defects. Mice having genetic perturbation of the Furin enzyme have demonstrated perimembranous and juxta-arterial ventricular septal defects, permitting the inference to be made that these defects can co-exist with defects occurring within the apical muscular septum. Based on developmental evidence, furthermore, all interventricular communications can be placed into one of three groups, namely, those which are perimembranous, juxta-arterial, and muscular. All of the defects are described based on their borders as seen from the morphologically right ventricle. Our focus here will be on those defects within the muscular ventricular septum, recognizing that such defects can co-exist with those that are perimembranous. We discuss the differentiation of multiple discrete defects from those referred to as the ‘Swiss cheese’ variant. As we show, appropriate surgical management requires understanding of the specific terminology, as the surgical approach may differ depending on the combination of the individual defects. Data from the Society for Thoracic Surgeons revealed that both mortality and morbidity were increased in the setting of multiple as opposed to solitary ventricular septal defects.