= Interventricular septum
The \b[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.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§19.1, Figures 19.6 and 19.9]{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.
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