Interventricular septum

The interventricular septum is a thick, muscular wall that separates the left and righ ventricle of the heart. It is directed obliquely backward and to the right, and is curved with the convexity toward the right ventricle: its margins correspond with the anterior and posterior longitudinal sulci.

It is typically divided into two parts:

1. Muscular part of interventricular septum

• Extent: Forms the inferior and majority (about 80%) of the septum.

• Thickness: Approximately 8–10 mm thick in adults, but thinner towards the apex.

• Composition: Made of myocardium arranged in spiraling layers, similar to the ventricular walls.

• Position: Lies between the anterior and inferior walls of the ventricles.

• Subdivisions:

  • Inlet septum, located near the atrioventricular valves, that extends posteriorly to the cardiac crux, separating the atrioventricular valves

  • Trabecular (or central) septum, the largest part, divides the anatomic bodies of the left and right ventricles

  • Infundibular septum that is located near the ventricular outflow tract, directly inferior to the junction between the commissure between the right and left coronary cusps of the aortic valve and the pulmonic commissure and distinct from the rest of the septum both in orientation and perfusion

• Surface features:

  • On the right ventricular side: The septum is marked by coarse trabeculae carneae and is more prominent because of the thinner right ventricular wall.

  • On the left ventricular side: It is smooth due to the thicker left ventricular wall.

2. Membranous Part

• Extent: Small, thin, and fibrous, forming the uppermost (about 20%) part of the septum.

• Dimensions: Measures only 1–2 mm in thickness.

• Position: Located just inferior to the right and non-coronary cusps of the aortic valve.

• Subdivisions:

  • Interventricular part: Between the ventricles.

  • Atrioventricular part (atrioventricular septum) : Between the right atrium and left ventricle.

• Relations:

  • Closely related to the fibrous skeleton of the heart, particularly the right fibrous trigone.

  • Lies near the bundle of His which passes through it.

Blood Supply

• Arteries:

  • Mostly supplied by septal branches of the left anterior descending artery (LAD).

  • Posterior third supplied by posterior interventricular artery (usually from the right coronary artery in right-dominant hearts).

• Venous drainage: Through the cardiac veins into the coronary sinus.

Innervation

• Supplied by the autonomic nervous system (sympathetic and parasympathetic fibers) through the cardiac plexus.