Author: Jana Vasković•Reviewer: Dimitrios Mytilinaios MD, PhDLast reviewed: September 30, 2021Reading time: 6 minutes


This write-up will talk about the great of the love (the epicardium, the myocardium and also the endocardium) and any clinical relations pertaining come them.

You are watching: The middle, muscular layer of the heart is called the:

In the same means that vehicles have actually their fuel pumps, ours body has the heart. The love is a muscular organ discovered in the center mediastinum the pumps blood transparent the body. That is housed in the pericardial sac, which protects it and assists v its mechanics.

Recalling from the heart anatomy, it has two atria and two ventricles that comprise elements and important steps for the heart cycle. However let’s take a look in ~ the heart histology; the is essential for expertise the duty of the heart. Histologically, the heart is do of 3 layers the tissue: epicardium, myocardium, and also endocardium.

Key facts around the class of the heart
EpicardiumVisceral class of serous pericardiumComprised of mesothelial cells and fat and also connective tissues
MyocardiumMuscle layerComprised of cardiomyocytes
EndocardiumLines inner surface ar of love chambers and also valvesComprised the a class of endothelial cells, and also a class of subendocardial connective tissue
Clinical relationEndocarditis

+ show all



The epicardium is the outermost class of the heart. That is in reality the visceral class of the serous pericardium, i beg your pardon adheres come the myocardium of the heart. Histologically, that is do of mesothelial cells, the exact same as the parietal pericardium. 

Below the mesothelial cells is a class of adipose and also connective tissue that binds the epicardium come the myocardium and also cushions the heart. Nerves and also blood vessels that supply the love are found in the epicardium. In ~ the root of an excellent vessels, the epicardium reflects back and proceeds as the parietal pericardium, forming an fastened pericardial sac. The sac is filled with serous pericardial fluid that prevents friction throughout heart contractions.

Once you"ve perfect learning about the class of the heart, start studying the key structures of the heart through our handy diagrams, worksheets and also quizzes



The myocardium is functionally the main constituent of the heart and also the thickest layer of all 3 heart layers. It is a muscle class that permits heart contractions. Histologically, the myocardium is comprised of cardiomyocytes. Cardiomyocytes have a single nucleus in the center of the cell, which help to distinguish them from skeletal muscle cell that have actually multiple nuclei distributed in the perimeter of the cell.

Cardiomyocytes are an extremely rich in glycogen deposits and mitochondria. This has a great functional significance since the myocardium is continuous contracting and also needs a good amount of energy at every times. Cardiomyocytes additionally contain yellow lipofuscin granules. They don’t have any details functional significance, however they are interesting since they are age markers because that the cell. The larger the cell, the an ext lipofuscin it has. 

Cardiomyocytes connect through special intercellular bridges called intercalated discs. The discs comprise of three components: adherens junction (fascia adherens), desmosomes (maculae adherentes) and also gap junctions (communicating junctions). These three components enable mechanical unified of cardiomyocytes and a direct pathway of spreading action potentials. Due to the fact that of this, the myocardium is observed together a form of syncytium, rather than a group of somewhat independent cells.

Although the framework of myocardium is the very same in the atria and ventricles, it is thicker in the ventricles. This is due to the better hydrostatic press that the ventricles need to overcome as soon as pumping the blood right into the systemic vessels. 


The endocardium is the innermost layer of the heart. It lines the inner surface of the heart chambers, consisting of the love valves. The endocardium has actually two layers. The inner layer present the heart chambers and is do of endothelial cells. Superiorly, is the second layer: a subendocardial connective organization which is constant with the connective tissue of the myocardium. Branches that the heart’s conduction device are immersed into the subendocardial layer.

Solidify your understanding with our quiz:

Clinical relations: Endocarditis

Endocarditis is an inflammation of the endocardium. Usually, it has actually an contagious etiology. It mostly affects currently damaged love valves and in many cases, is brought about by the bacteria Streptococcus viridans. In the instance of a healthy heart, the pathogenic bacteria is Streptococcus aureus. No matter what bacteria is the cause, pathogenesis is the same. As soon as the bacteria lugged by the bloodstream will the heart valves, they invade the endocardium. Climate they reason the damage of heart tissue, which leads to the development of friable vegetations written of necrotic debris (destructed love cells), thrombi, and also microorganisms. Components of the vegetation deserve to be loosened by the bloodstream and also disseminated throughout the body, forming an additional deposits the infection. If the resulting in bacteria is really virulent, the endocarditis has actually a fulminant course and often a fatal outcome. On the various other hand, as soon as the bacteria space not for this reason virulent they deserve to persist for some time in the heart causing valves deformities. 

It is interesting that Streptococcus viridans is normally uncovered in the dental cavity, whereby the easiest way for it to reach the love and type vegetations top top damaged valves is throughout a stomathology procedure. Because that this reason, it is crucial to educate your doctor if you have a valve problem, so they can prescribe antibiotics for precautions. 

Usual symptoms of endocarditis room flu-like signs, heart murmur, night sweating, shortness the breath, and also chest pain during breathing. Transmittable endocarditis is treated by intravenous antibiotics because that 2 come 6 weeks. If the condition has significantly damaged the heart valves, it is shown to do a valve instead of or fix surgery. 



Ross, M. H., Pawlina, W. (2011). Histology (6th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.Mescher, A. L. (2013). Junqueira’s basic Histology (13th ed.). Brand-new York, NY: McGraw-Hill Education.Kumar, V., Abbas, A. K., Aster, J. C. (2013). Robbins straightforward Pathology (9th ed.). Philadelphia, PA: Elsevier Saunders.

Layers that the heart: desire to learn much more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are right here to obtain you height results faster.

See more: How To Reduce Lag On Tf2 - :: Team Fortress 2 General Discussions

What execute you favor to find out with?

“I would certainly honestly say the reduced my research time in half.”–Read more.

Kim Bengochea, Regis University, Denver