In the heart, the<unk>  is the innermost layer of tissue that lines the chambers of the heart. Its cells, embryologically and biologically, are similar to the<unk> thelial cells that line blood vessels.
The<unk>  overlies the much more voluminous myocardium, the muscular tissue responsible for the contraction of the heart. The outer layer of the heart is termed epicardium and the heart is surrounded by a small amount of fluid enclosed by a fibrous sac called the pericardium.
Endocardium
Ventricle 
Epicardium
Cardiac muscle
Base of the heart
Papillary muscle
Heart valve
Serous pericardium