What are the Layers of the Heart Wall?

Christina Keathley, Sarah Phenix
  • Author
    Christina Keathley

    Christina graduated with a Master's in biology from the University of Louisiana at Lafayette. She is a current PhD student in biology at Wake Forest University, and has been teaching undergraduate students anatomy and physiology for the last two years.

  • Instructor
    Sarah Phenix
Learn about the pericardium and the three layers of the heart wall. Discover distinctive features of the pericardium, epicardium, myocardium, and endocardium. Updated: 09/23/2021

Table of Contents


What Are the Layers of the Heart?

The heart is an amazing organ. Its main function is to pump blood throughout the body, which continues the flow of fresh oxygen to various tissues and systems. The heart is partially so efficient because of its shape. The orientation of the different compartments of the heart allows for deoxygenated blood to enter, pass to the lungs to receive oxygen, and exit back to the body. As the heart pumps, the alignment of the valves and compartments of the heart prevent the oxygen-rich blood and oxygen-depleted blood from mixing and flowing backward.

The heart's strong contractions are the driving force of the circulatory system. With each contraction, blood is forced out of one area and into the next. These contractions are the result of strong muscle tissues that compose the walls of the heart. The heart's walls are divided into four layers. Together, these layers both compose the muscle tissue that makes up the heart and provides essential functions to assist in muscular contractions. The layers of the heart are as follows:

  • Pericardium, or the layer surrounding the heart
  • Epicardium, the outside layer of the heart
  • Myocardium, the middle layer of the heart
  • Endocardium, the innermost layer of the heart.

The myocardium composes the majority of the heart wall (tan), while endocardium composes the inner lining and valves.

A diagram of the heart with 2 of the 3 layers of the heart illustrated.

In this lesson, investigate the layers of the heart wall to better understand how they function and contribute to the circulatory system. Continue reading to answer the following questions:

  • What are the three layers that compose the heart wall, and what is the function of the outermost layer?
  • How do the three layers function together within the circulatory system?
  • What is the muscular layer of the heart wall called?

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Pericardium: Outermost Layer of the Heart

As the heart beats, it expands to fill with blood and constricts to expel blood out. Because the heart changes in size as it functions, its movement would likely cause friction with other organ systems and tissues within the chest cavity. Excess friction would wear down tissue and eventually decrease the health and efficacy of the exposed tissues. To curb this potential issue, the heart is contained within a thin sac referred to as the pericardium. The pericardium contains the parietal pericardium and epicardium.

The pericardium is a layer of connective tissue filled with lubricating fluids. These fluids (called serous fluids) reduce the friction within the pericardial sac and protect the heart from potential pathogens. The production of these fluids is controlled by the epicardium and parietal pericardium. In addition to protection and lubrication, the pericardium is important in maintaining the position of the heart within the body cavity. It also prevents the heart from stretching too much by restricting the amount it can expand.

Three Layers of the Heart Wall

While the pericardium does not compose the actual heart, the heart wall is composed of three additional yet separate layers. These layers work together to form the major structure of the heart and allow it to function after endless hours of pumping. The three layers of the heart, as discussed above, are the epicardium, myocardium, and endocardium.

Epicardium: Outermost Layer of the Heart Wall

The outside surface of the heart is referred to as the epicardium. "Epi" refers to outside, and "cardium" refers to the heart. Thus, the epicardium is the outside of the heart. The epicardium is sometimes referred to as the visceral pericardium. This is because it is composed of connective tissue that, in part, connects to the pericardium and forms its second layer.

The epicardium has an important function within the cardiovascular system. While the heart's main job may be to circulate blood, it does not benefit directly from the blood it pumps. Instead, it must receive freshly oxygenated blood via a system of vessels, like all other organs in the body. This fresh blood is delivered through a system of blood vessels that reside within the epicardium. Thus, the epicardium is largely responsible for the delivery of fresh oxygen and nutrients to the cardiac tissue of the heart.

Myocardium: Muscular Middle Layer of the Heart Wall

The myocardium is the middle layer of the heart and composes most of the heart's tissue. The myocardium is composed of muscular tissue and generates the contractions that control the pumping of the heart. This muscle is known as cardiac muscle and differs from the other types of muscles in the body. Unlike skeletal muscle, cardiac muscle tissue is involuntary and contains intercalated discs. These discs increase the rate at which electrical stimuli travel through the heart, generating more uniform contractions. In addition, cardiac muscle does not fatigue and can thus contract repetitively without becoming tired or sore. The thickest section of the myocardium is found in the right ventricle of the heart, which requires the strongest contractile forces.

Cardiac muscle is a specialized type of muscle that does not fatigue and transmits electrical impulses quickly between fibers.

A microscopic photograph of cardiac muscle within the heart.

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Frequently Asked Questions

What are the 3 layers of the wall of the heart?

The three layers of the heart wall are the epicardium, myocardium, and endocardium. There is a fourth layer that envelopes the heart called the pericardium.

What are the three layers of the heart and their functions?

The epicardium is the outer layer that contains blood vessels. The myocardium is the middle layer that is composed of contractile tissues. The endocardium is the innermost layer and composes the valves, inner lining of the chambers, and contains vessels and nerves.

Is pericardium and epicardium the same?

The pericardium is a layer of tissue that surrounds the heart and contains fluid to reduce friction. While the epicardium is technically an extension of the pericardium, it is often referred to as a separate layer because it composes part of the heart's wall.

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