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.