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


This article will discuss the great of the heart (the epicardium, the myocardium and the endocardium) and also any clinical relationships pertaining come them.

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In the same method that vehicles have their fuel pumps, our body has actually the heart. The heart is a muscular organ discovered in the center mediastinum the pumps blood transparent the body. It is housed in the pericardial sac, i beg your pardon protects it and also assists with its mechanics.

Recalling indigenous the heart anatomy, it has two atria and two ventricles that consist of elements and important measures for the love cycle. However let’s take a look in ~ the love histology; it is necessary for understanding the role of the heart. Histologically, the heart is make of 3 layers of tissue: epicardium, myocardium, and endocardium.

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

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The epicardium is the outermost great of the heart. It is actually the visceral class of the serous pericardium, which adheres come the myocardium that the heart. Histologically, it is make of mesothelial cells, the exact same as the parietal pericardium. 

Below the mesothelial cell is a layer of adipose and connective organization that binds the epicardium come the myocardium and cushions the heart. Nerves and blood vessels that supply the love are found in the epicardium. In ~ the roots of an excellent vessels, the epicardium reflects back and continues as the parietal pericardium, forming an attached pericardial sac. The sac is filled through serous pericardial liquid that prevents friction throughout heart contractions.

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The myocardium is functionally the key constituent that the heart and the thickest class of all three heart layers. It is a muscle class that permits heart contractions. Histologically, the myocardium is comprised of cardiomyocytes. Cardiomyocytes have actually a solitary nucleus in the facility of the cell, which helps to differentiate them indigenous skeletal muscle cell that have multiple nuclei dispersed in the periphery of the cell.

Cardiomyocytes are very rich in glycogen deposits and also mitochondria. This has actually a an excellent functional significance due to the fact that the myocardium is continually contracting and also needs a good amount of energy at all times. Cardiomyocytes likewise contain yellow lipofuscin granules. Castle don’t have actually any particular functional significance, however they space interesting since they are age markers for the cell. The older the cell, the much more lipofuscin that has. 

Cardiomyocytes communicate through unique intercellular bridges called intercalated discs. The discs make up of 3 components: adherens junction (fascia adherens), desmosomes (maculae adherentes) and also gap junctions (communicating junctions). These 3 components enable mechanical unified of cardiomyocytes and also a straight pathway of spreading activity potentials. Since of this, the myocardium is observed together a kind of syncytium, quite than a team of rather independent cells.

Although the framework of myocardium is the exact same in the atria and also ventricles, that is more thick in the ventricles. This is due to the better hydrostatic push that the ventricles need to overcome once pumping the blood into the systemic vessels. 


The endocardium is the innermost layer of the heart. That lines the inner surfaces of the love chambers, consisting of the love valves. The endocardium has two layers. The inside layer currently the love chambers and also is made of endothelial cells. Superiorly, is the second layer: a subendocardial connective tissue which is constant with the connective tissue of the myocardium. Branches the the heart’s conduction mechanism are immersed right into the subendocardial layer.

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Clinical relations: Endocarditis

Endocarditis is an inflammation the the endocardium. Usually, it has actually an contagious etiology. It mainly affects currently damaged heart valves and in most cases, is brought about by the bacteria Streptococcus viridans. In the case of a healthy and balanced heart, the pathogenic bacteria is Streptococcus aureus. No matter what bacteria is the cause, pathogenesis is the same. Once the bacteria carried by the bloodstream get the heart valves, they invade the endocardium. Then they reason the devastation of love tissue, which leader to the development of friable vegetations written of necrotic debris (destructed heart cells), thrombi, and microorganisms. Parts of the vegetation have the right to be loosened by the bloodstream and also disseminated throughout the body, forming an additional deposits the infection. If the leading to bacteria is an extremely virulent, the endocarditis has a fulminant course and also often a deadly outcome. Top top the various other hand, when the bacteria space not therefore virulent they can persist for some time in the heart resulting in valves deformities. 

It is exciting that Streptococcus viridans is normally uncovered in the dental cavity, where the easiest way for it to reach the love and type vegetations on damaged valves is throughout a stomathology procedure. For this reason, that is important to inform your physician if you have a valve problem, for this reason they might prescribe antibiotics because that precautions. 

Usual symptom of endocarditis room flu-like signs, heart murmur, night sweating, shortness of breath, and also chest pain throughout breathing. Transmittable endocarditis is cure by intravenous antibiotics because that 2 come 6 weeks. If the condition has considerably damaged the love valves, that is shown to perform a valve replacement 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.). New York, NY: McGraw-Hill Education.Kumar, V., Abbas, A. K., Aster, J. C. (2013). Robbins basic Pathology (9th ed.). Philadelphia, PA: Elsevier Saunders.

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