 Interventricular septum

The interventricular septum is the partition separating the cavities of the right ventricle and left ventricle. It is internal to the heart, unlike the external anterior interventricular sulcus and posterior interventricular sulcus. The distinction can be seen by comparing an intact surface view with an opened view of the ventricular chambers.^[ref]

An intact partition lets the two ventricular pumps operate at different blood pressure values without a direct open route between their cavities. An elementary physical model makes the role clear: if a hypothetical opening connected two chambers, a pressure gradient across that opening could drive an additional blood flow. Conservation would then require a term for transfer between chambers, in addition to the flow through their respective heart valves. This thought experiment explains why a partition is part of the circulation's topology, rather than merely a line on an anatomical drawing.

The interventricular septum also belongs to the mechanically connected ventricular structure. Consequently, measuring right ventricular ejection fraction and measuring left ventricle function describe two chambers in one coupled heart, rather than two unrelated pumps. For an anatomical identification exercise, first find the two cavities, then identify their common separating wall; locating a surface groove alone does not establish the wall's thickness or internal structure.