These images show that the interventricular communication is not necessarily the same thing as the ventricular septal defect. In Figure 2A, we show a heart with double outlet right ventricle sectioned in four-chamber fashion, showing the aorta arising exclusively from the right ventricle, but with its cranial margin formed by fibrous continuity between the leaflets of the aortic and mitral valves. It is the space between this margin and the crest of the apical muscular septum that is the true interventricular communication. This space (double headed red arrow), however, can never be closed, since such closure would wall off the aorta from the left ventricle. As shown in Panel B, in which the free wall of the right ventricle has been lifted away to reveal a defect in a heart with the larger part of the aortic root supported within the right ventricle, in other words effectively a double outlet ventriculo-arterial connection, the outlet septum is exclusively a right ventricular structure, and is fibrous rather than muscular. The yellow dots show the margins of the defect that would be closed so as to place the aortic root in continuity with the cavity of the left ventricle. It is this curved surface that represents the ventricular septal defect, albeit that it is not the geometric interventricular communication.