What Is It, Functions, and More

Author:Lily Guo

Editors:Alyssa Haag,Józia McGowan, DO

Illustrator:Jillian Dunbar

Copyeditor:David G. Walker

What is the epicardium?

The epicardium 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 the roots of the coronary vessels emerging from it, including the aorta, the superior vena cava, and inferior vena cava

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.

Where is the epicardium located?

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

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What is the function of the epicardium?

There are many functions of the epicardium aside from its main protective role as the outer surface of the heart. It 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 can 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 is 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). The visceral layer of the serous pericardium is also known as the epicardium. The main purpose of all of the aforementioned layers are the same: to protect the heart and assist in contractration. 

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

The epicardium, or the innermost layer of the pericardium, is the outermost layer of the heart itself. It is composed of mesothelial cells, fat, and connective tissue. It is adjacent to the myocardium, the middle muscular layer. The innermost layer is referred to as the endocardium. The epicardium comprises part of the pericardium, forming the visceral portion of the serous layer. The epicardium serves many functions, including protecting the heart, producing factors that help the cardiac cells properly develop, and ensuring proper response to cardiac cell injury. 

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Related links

Cardiovascular system anatomy and physiology
Anatomy of the heart
Pericarditis and pericardial effusion

Resources for research and reference

Gittenberger-de Groot, A. C., Winter, E. M., Bartelings, M. M., Jose Goumans, M., DeRuiter, M. C., & Poelmann, R. E. (2012). The arterial and cardiac epicardium in development, disease and repair. Differentiation, 84(1), 41–53. DOI: 10.1016/j.diff.2012.05.002 

Gurarie, M. What to know about the endocardium. In Verywell Health. Retrieved September 14, 2021, from 

Layers of the Heart Walls. (2020, August 13). Retrieved September 13, 2021, from

Limana, F., Zacheo, A., Mocini, D., Mangoni, A., Borsellino, G., Diamantini, A., De Mori, R., Battistini, L., Vigna, E., Santini, M., Loiaconi, V., Pompilio, G., Germani, A., & Capogrossi, M. C. (2007). Identification of myocardial and vascular precursor cells in human and mouse epicardium. Circulation Research, 101(12), 1255–1265. DOI: 10.1161/circresaha.107.150755 

Quijada, P., Trembley, M. A., & Small, E. M. (2020). The role of the Epicardium during Heart development and repair. Circulation Research, 126(3), 377–394. DOI: 10.1161/circresaha.119.315857 

Vaskovi, J. (2021, August 30). Pericardium. In Kenhub. Retrieved September 14, 2021, from