endocardium

The endocardium is the smooth, slippery wallpaper lining the inside of the heart. Like the non-stick coating inside a pipe, it gives blood a frictionless surface to glide over so clots are less likely to form.

It is the thin innermost layer of the heart wall, covering the inside of all four chambers and forming the surface of the heart valves. It is continuous with the endothelium that lines the blood vessels, so the heart's inner surface and the inside of the arteries and veins form one unbroken lining.

Because it is the layer in direct contact with blood, the endocardium is where certain infections take hold. Infective endocarditis is an infection of this lining, often involving the valves, where bacteria form clumps called vegetations. A healthy, intact endocardium is one of the body's defenses against such infection and against clot formation.