
Endocardium
The endocardium (black arrows) lines the heart chambers and is continuous with the tunica intima of blood vessels. It consists of a simple squamous epithelium (endothelium), an underlying layer of subendothelial connective tissue that may contain smooth muscle fibers, and a deeper layer of subendocardial connective tissue. Elements of the conducting system of the heart, Purkinje fibers, are located in the subendocardial connective tissue. The endocardium is thicker in the atria than in the ventricles. 10x, 400x

Endocardium
The endocardium (black arrows) lines the heart chambers and is continuous with the tunica intima of blood vessels. It consists of a simple squamous epithelium (endothelium), an underlying layer of subendothelial connective tissue that may also contain smooth muscle fibers, and a deeper layer of subendocardial connective tissue. Elements of the conducting system of the heart, Purkinje fibers, are located in the subendocardial connective tissue. The endocardium is thicker in the atria than in the ventricles. 10x, 400x

- Endothelium
The endocardium (black arrows) lines the heart chambers and is continuous with the tunica intima of blood vessels. It consists of a simple squamous epithelium (endothelium), an underlying layer of subendothelial connective tissue that may also contain smooth muscle fibers, and a deeper layer of subendocardial connective tissue. Elements of the conducting system of the heart, Purkinje fibers, are located in the subendocardial connective tissue. The endocardium is thicker in the atria than in the ventricles. 10x, 400x

- Subendothelial connective tissue
The endocardium (black arrows) lines the heart chambers and is continuous with the tunica intima of blood vessels. It consists of a simple squamous epithelium (endothelium), an underlying layer of subendothelial connective tissue that may also contain smooth muscle fibers, and a deeper layer of subendocardial connective tissue. Elements of the conducting system of the heart, Purkinje fibers, are located in the subendocardial connective tissue. The endocardium is thicker in the atria than in the ventricles. 10x, 400x

- Subendocardial connective tissue
The endocardium (black arrows) lines the heart chambers and is continuous with the tunica intima of blood vessels. It consists of a simple squamous epithelium (endothelium), an underlying layer of subendothelial connective tissue that may also contain smooth muscle fibers, and a deeper layer of subendocardial connective tissue. Elements of the conducting system of the heart, Purkinje fibers, are located in the subendocardial connective tissue. The endocardium is thicker in the atria than in the ventricles. 10x, 400x

Cardiac muscle fibers of the myocardium
The endocardium (black arrows) lines the heart chambers and is continuous with the tunica intima of blood vessels. It consists of a simple squamous epithelium (endothelium), an underlying layer of subendothelial connective tissue that may also contain smooth muscle fibers, and a deeper layer of subendocardial connective tissue. Elements of the conducting system of the heart, Purkinje fibers, are located in the subendocardial connective tissue. The endocardium is thicker in the atria than in the ventricles. 10x, 400x

Image credit >
Images from the University of Cincinnati slide collection.