Basal loop.
It predominantly comprises the transverse muscle fibers, subdivided into
two segments, right (RS) and left (LS). The RS forms the free wall of
the right ventricle (RV) from the anterior to the posterior
interventricular sulcus, including the infundibulum and the root of the
pulmonary artery. The LS forms part of the free wall of the left
ventricle (LV) and begins in continuity with the posterior
interventricular sulcus, accompanied during its course from the left
marginal artery to the base of the LV and the left fibrous trigone.