THE FIBROUS SKELETON
Just like the human body, the heart has its own skeleton. The four cardiac cavities are attached to it.
There are four rigid fibrous rings and a small extension in the lower center. This extension is the beginning of the structure that separates the two ventricles (the membranous septum).
These rings, besides being the anchors of the cardiac cavities, are the support for the four cardiac valves.
The rigid fibrous rings cannot be increased in size.
In case of valve replacement, the size of the new valve is selected according to the diameter of the fibrous ring into which the valve must be inserted.