Left fibrous trigone

The left fibrous trigone (trigonum fibrosum sinistrum) in the heart is a dense connective tissue structure of the fibrous skeleton located between the left fibrous ring (mitral annulus) and the aortic fibrous ring. It forms part of the central fibrous body and provides a strong area of continuity between these rings, contributing to the structural integrity of the cardiac base.

In dogs, the left fibrous trigone is smaller than the right and lies in the triangle between the aortic and left atrioventricular ostia to the left of the right fibrous trigone.

This trigone serves as an important anchoring point for valve structures and adjacent myocardial fibers, and it plays a role in maintaining the mechanical stability of the left heart while participating in the electrical insulation between atrial and ventricular myocardium.