And together these two layers play a role in lubricating our heart along with the fluid found within the pericardial cavity. Now, the thickest segment of the heart is the myocardium and this is the middle portion. This consists of specialized heart cells known as myocytes, also known as cardiac muscle cells. And these are the cells that are responsible for contracting and creating that hydrostatic pressure that is needed to pump all that blood through all the blood vessels of our body. Now, the innermost portion of the heart that is in direct contact with the blood of our chambers, found inside the chambers of the heart, this is known as the endocardium. And the endocardium consists of endothelial cells of simple squamous opel cells that are in direct contact with the blood found inside our chambers.