Endocardium

The endocardium is the thin, smooth membrane composed of a specialized endothelial cell layer that lines the inner surface of the heart chambers, forming the innermost layer of the heart wall. It is composed of endocardial cells, which are specialized endothelial cells that develop during embryogenesis and are maintained throughout life.

The endocardium consists of a single layer of specialized endothelial cells that directly contact the blood within the cardiac chambers. During heart development, the endocardium is separated from the outer myocardial layer by a thick extracellular matrix called cardiac jelly. This endothelial lining is continuous with the endothelium of the blood vessels entering and leaving the heart.