The endocardium is a thin, smooth layer of tissue that lines the interior of the heart chambers. It is composed of endothelial cells and connective tissue, providing a smooth surface that helps blood flow easily through the heart. This layer also plays a role in regulating the heart's function and protecting it from infections. In addition to lining the heart, the endocardium is involved in the formation of heart valves, which control blood flow between the chambers. Any damage or inflammation to the endocardium can lead to conditions such as endocarditis, an infection that can affect heart function and overall health.