Left ventricle

The left ventricle (ventriculus sinister) of the heart is the thick-walled, caudodorsal cardiac chamber responsible for pumping oxygenated blood into the systemic circulation via the aorta. Its morphology reflects its function as a high-pressure pump.

Topography and external features

The heart lies obliquely within the middle mediastinum, extending approximately from the 3rd to the 6th intercostal spaces. The left ventricle forms most of the caudal (diaphragmatic) surface and the left lateral surface of the heart, as well as the cardiac apex. Externally, the LV is separated from the right ventricle by the paraconal interventricular groove (on the auricular surface) and the subsinuosal interventricular groove (on the atrial surface), both of which contain coronary vessels.

Internal morphology

Cavity and wall

The left ventricular cavity is conical, with a broad base at the atrioventricular junction and a narrow apex. The wall is markedly thicker than that of the right ventricle (approximately two to three times thicker in healthy adult dogs), reflecting the higher resistance of systemic circulation. The myocardium is composed of spirally arranged cardiac muscle fibers that contribute to torsional contraction.

Inflow tract

Blood enters the left ventricle from the left atrium through the left atrioventricular (mitral or bicuspid) valve. The mitral valve consists of two cusps (septal and parietal/mural). The free edges of these cusps are attached via chordae tendineae to papillary muscles, which prevent prolapse of the valve during systole. Typically, two major papillary muscles (subauricular and subatrial) arise from the ventricular wall.

Trabeculae carneae

The internal surface of the left ventricle is lined by fine trabeculae carneae, which are less coarse and fewer than those in the right ventricle. These muscular ridges are most prominent near the apex.

Interventricular septum

The interventricular septum forms the medial wall of the left ventricle and bulges slightly into the right ventricular lumen due to higher left-sided pressures. It consists predominantly of a thick muscular part and a small membranous part located near the aortic root. The septum contains components of the cardiac conduction system.

Outflow tract

The outflow portion, known as the aortic vestibule, is smooth-walled and located cranially and to the right of the inflow tract. It leads to the aortic valve. The transition from the trabeculated inflow region to the smooth outflow tract is gradual and less distinctly separated than in the right ventricle.

Vascular supply

The left ventricle receives its blood supply primarily from branches of the left coronary artery (notably the paraconal interventricular branch and circumflex branch), although the exact coronary dominance pattern may vary among individuals and species.

Functional considerations

The left ventricle generates systemic arterial pressure. During systole, coordinated contraction of the thick myocardium produces a twisting motion that enhances ejection efficiency. In diastole, active relaxation and ventricular compliance allow efficient filling from the left atrium.