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Cardiac skeleton

The cardiac skeleton or anulus fibrosus is not a bony structure like the human body’s actual skeleton, but a fibrous structural support for the heart chambers.

This article will highlight the anatomical importance of this structure and its functions, as well as describing its architecture within the heart and a potential pathological condition.

  1. Functions
  2. Anatomy
  3. Clinical notes
  4. Sources
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The cardiac skeleton has four major functions. Firstly, it anchors the heart valve cusps to the interior walls of the heart, which stabilizes the thin petal like sections of the valves and prevents them from malfunctioning, which could be potentially fatal. Secondly, it keeps the atrioventricular valves and the semilunar valves of the heart open, without allowing them to distend. This limits the risk of potential tears in the valvular cusps and prevents backflow of the blood into the chamber it was released from.

Thirdly, it provides a point of insertion for the bundles of the heart muscle and effectively separates the atria from the ventricles in order to do so. Lastly, it acts as an electrical insulator by preventing the radiating electrical impulses from passing through the atrial muscles to the ventricles, thus preventing a singular contraction, which in turn allows the ventricles to fill up with blood.


The cardiac frame is composed of a dense connective tissue network that forms a fibrous skeleton. It reinforces the myocardial walls internally and anchors the cardiac muscle. The thickness of the collagen and elastin fibers of the anulus fibrosus varies from area to area and consists of four rings, two trigones and one ligament. The exact position of this scaffolding can be clearly seen on the external side of the heart, where the great vessels exit and enter it, within the coronary sulcus.

Fibrous ring of tricuspid valve - cranial view
Fibrous ring of tricuspid valve (cranial view)

The left fibrous ring encircles the bicuspid valve and the right fibrous ring surrounds the tricuspid valve. The pulmonary ring corresponds to the pulmonary valve as does the aortic ring to the aortic valve. The right fibrous trigone runs around both the right fibrous ring and the aortic ring together, whereas the left fibrous trigone runs around the left fibrous ring and the aortic ring. Lastly, a tendinous band known as the ligament makes up the posterior border of the conus arteriosus.

Left fibrous trigone (cranial view)

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