Endocardium: What is it? Types of Layers, Functions and Associated Conditions

It is the thin inner layer of the heart wall.

This layer covers the internal chambers of the heart, covers the valves of the heart and is continuous with the endothelium of the great blood vessels. The endocardium of the atrium of the heart consists of smooth muscle, as well as elastic fibers.

Now, the heart has some different coatings associated with it, so to better understand where the endocardium is, let’s make a quick review of the anatomy of the heart.

The heart is part of the cardiovascular system. The cardiovascular system, sometimes called the circulatory system, is made up of the heart and arteries, veins and capillaries that extend throughout the body.

The outer part of the heart is lined with a thin tissue called the pericardium. Below the pericardium, you have the fibrous pericardium and the serous pericardium.

Beneath the serous pericardium is the epicardium. Below the epicardium there is a thick muscular layer called myocardium. Then, finally, we reach the thin inner layer of the heart, which is the endocardium.

Endocardium layers

The endocardium covers both the atria, the ventricles and all the valves of the heart. This thin and delicate lining of the heart is composed of three layers:

Connective subendocardial tissue:

The first layer contains the connective tissue and the Purkinje fibers. Through the cardiac muscle, the Purkinje fibers help conduct electricity and the connective tissue helps the endocardium to attach to the myocardium.

Fibro-elastic tissue:

The second layer contains a thin muscular layer and has more connective tissue, which is why it is thickest in the atria than in the ventricles.

Fibers of collagen, elastic tissue and some smooth muscle are the components of this layer


The third layer contains vascular endothelium that is formed by special cells that line the inside of the circulatory system.


This thin but important layer fulfills three fundamental functions in the cardiovascular system.

1) The endocardium is responsible for the blood flowing freely throughout the tissues, as it provides a smooth surface for the interior of the heart.

Thanks to the endocardium, the blood components do not adhere to the walls of the heart, if this happens it could cause tissue damage or induce blockages. This membrane also helps prevent the heart tissues from sticking when they beat.

2) By containing the Purkinje fibers, the endocardium is essential for the heart to beat.

The Purk fibers transmit the electrical signals to the whole heart. This electricity in turn helps the heart muscles contract.

3) The endocardium has additional layers around the valves of the heart (atrio-ventricular and semi-lunar), which join with the valves to make them stronger and work better.

Symptoms in the endocardium

The endocardium is vulnerable to damage from conditions such as rheumatic heart disease and valvular heart disease. These conditions can cause irritation that inflames the endocardium. An infection of the endocardium can lead to a condition known as endocarditis .

Endocarditis is typically the result of infection of the heart valves or the endocardium by certain bacteria, fungi or other microbes. Endocarditis is a serious disease that can be fatal.

Valvular disease:

Diseases of the valves of the heart take two varieties of name, one that refers to the name of the valves affected, and the other to the nature of the disease.

In relation to the valves themselves there are said to be four varieties of diseases, namely:

Aortic disease: Insufficiency of the semilunar or aortic valves; the valves that lie between the aorta, or the large outgoing artery, and the left ventricle, or the large forced structure of the heart.

Mitral disease: Large bicuspid or mitral valve disease; the valve between the left atrium and the left ventricle of the heart.

Pulmonary valvular disease: Insufficiency of small semilunar or pneumonic valves; the valves that are between the pulmonary artery, the artery that goes to the lungs from the right ventricle of the heart and the right ventricle.

Tricuspid disease: Difference of the tricuspid valve; the valve that is between the right atrium and the right ventricle of the heart.

Of these valvular structures, the valves on the left side of the heart, the aorta and the mitral valve are much more prone to disease than the valves, pulmonary and tricuspid, on the right side.

It can be said that valvular disease on the right side is relatively rare, a fact that I have tried to explain in my experimental research on “the synthesis of valvular disease”, by showing that in most cases valvular disease is due to irritation.

Valvular diseases are, by far, the most prevalent in people of rheumatic constitution, and are the frequent consequences of acute rheumatic fever .

Divided according to the nature of the disease, valvular heart conditions are:

Vegetations:  In which small growths, similar to fungoid vegetations, occur at the margins or thin surfaces of the valves.

Thickening:  In which the fibrous tissue of the valvular structure thickens and condenses, so that the valves do not act with due ease of opening and closing, for the admission or stoppage of the blood flow.

Fat and calcareous  degenerations : Fat degeneration is called atheroma, the calcaneus is called ossification.

They consist of changes in which the valve structures are transformed, in part, into a form of fatty structure, or into a bone substance, and in which the regulating movements of the valves are extremely impeded.

Aneurysm :  Disease that consists of enlargement, dilatation, of the valves, or of enlargement of the vessels through which blood is supplied to the valves.

Laceration:  Accidental tearing of the valvular structure, under great excitement or tension. In very rare cases, this accident has occurred where there has been a very healthy valve condition.

Dilatation of the orifice of the valves: A condition in which the opening or orifice of the valves is very dilated, so that the curtains of the valves that leave the orifice become Inca to fulfill perfectly in the act of closing.

This condition is common in cases in which the heart is subjected for many years to severe stress due to excessive action, and where all its structures are dilated.

In certain of these forms of valvular disease, regurgitation of the blood is not often detected by the physician.

The term means that, due to the imperfect action of the valves, they do not close efficiently, so that the blood they must prevent from returning and that they must direct in their course, flows backwards or regurgitates in the cavity from which it originates.