ventricular septal defect muscular ventricular septal defect 2010-09-27T04:13:52Z Fyler:1320 MP:0010420 MPheno.ontology Swiss-cheese septum VSD, Type 4 abnormal communications between the two lower chambers of the heart, involving the muscular septum and often occurring as multiple communications, and includes central muscular or midmuscular, apical, or marginal communications when the defect is along the RV-septal junction; any single defect observed from the LV aspect may have several openings on the RV aspect csmith mVSD trabecular ventricular septal defect ventricular septal defect, muscular abnormal interventricular septum muscular part morphology