Epicardium · What Is It, Functions, and More

Published: Sep 26, 2025
Author: Lily Guo, MD•
Editor: Alyssa Haag, MD•
Editor: Józia McGowan, DO•
Editor: Maria Giulia Boemi, MD
Illustrator: Jillian Dunbar•
Copyeditor: David G. Walker
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What is the epicardium?

The epicardium, also known as the visceral layer of the serous pericardium, refers to the outermost protective layer of the heart. The epicardium is composed of mesothelium, a cell type that covers and protects most of the internal organs of the body as well as fat and connective tissue. The epicardium predominantly surrounds the heart and contains coronary vessels , which supply blood and oxygen to the tissues of the heart.  

The other two layers surrounding the heart include the myocardium (i.e., the middle muscular layer that supports the pumping capabilities of the heart) and the endocardium, or the innermost layer.  

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Where is the epicardium located?

The epicardium is located adjacent to the myocardium and surrounds the heart.  

What is the function of the epicardium?

The epicardium is the innermost layer of the pericardium, which is the membrane enclosing the heart, and serves a protective function. Other functions of the epicardium include providing signals for proper heart formation and maturation within the embryo and secreting factors that are important for proliferation and survival of cardiomyocytes (i.e., the cells that make up the heart muscle). The cells derived from the epicardium may also act as cardiac cell progenitors, or cells that can become many other different types of cells. Lastly, epicardial signals play a role in the heart’s injury response to heart disease, namely myocardial infarctions (i.e., heart attack), and subsequent heart regeneration.  

What is the difference between the epicardium and the pericardium?

The epicardium is part of the pericardium. It’s the innermost layer and is referred to as the visceral layer of the serous pericardium. The main difference is the nomenclature and the specific layers of the heart that they are describing. The pericardium consists of three separate layers that envelope the heart: an outer fibrous layer (i.e., fibrous pericardium), the parietal layer of the serous pericardium, and the visceral layer of the serous pericardium. The two serous layers are divided by the pericardial cavity, which contains pericardial fluid (i.e., a layer of fluid which serves to separate the heart from other structures, protect the heart against infection and blunt trauma, and lubricate the heart's movements).  

What are the most important facts to know about the epicardium?

The heart consists of three layers: the epicardium, myocardium (i.e., the middle muscular layer), and endocardium (i.e., the innermost layer). The epicardium is both the outermost layer of the heart itself and innermost layer of the pericardium, which is a protective membrane that surrounds the heart. The epicardium is composed of mesothelial cells, fat, and connective tissue. It serves many functions, including protecting the heart, producing factors that help cardiac cells develop properly, and ensuring proper response to cardiac cell injury. 

Key Takeaways

Definition 

The epicardium, or visceral layer of the serous pericardium, is both the outermost layer of the heart itself and the innermost layer of the pericardium. 

Location

- Adjacent to the myocardium  

- Surrounds the heart 

- Composed of mesothelial cells 

Function 

- Protects the heart 

- Provides signals for embryonic heart formation and maturation 

- Secretes factors for cardiomyocyte proliferation and survival 

- Responds to heart injury, helps with regeneration 

Pericardium

- Pericardium 

     - Protective membrane surrounding the heart 

- Epicardium is innermost layer  

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Anatomy of the heart

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Cardiovascular system anatomy and physiology

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Endocarditis

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Pericarditis and pericardial effusion

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References

Cao Y, Duca S, Cao J. Epicardium in heart development. Cold Spring Harb Perspect Biol. 2020;12(2):a037192. Published 2020 Feb 3. doi:10.1101/cshperspect.a037192 


Gittenberger-de AC, Winter EM, Bartelings MM, Goumans MJ, DeRuiter MC, Poelmann RE. The arterial and cardiac epicardium in development, disease and repair. Differentiation. 2012;84(1):41-53. doi:https://doi.org/10.1016/j.diff.2012.05.002 


Quijada P, Trembley MA, Small EM. The role of the epicardium during heart development and repair. Circ Res. 2020;126(3):377-394. doi:10.1161/CIRCRESAHA.119.315857 


Standring S, ed. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2020.