In the outermost layer of the heart wall, the epicardium , observe the superficial layer of mesothelium, the visceral pericardium , which has not always been preserved, and the underlying connective tissue with its rich content of adipose tissue containing branches of the coronary arteries. The epicardium may also be seen in slide 105. In slide 103 or 105 observe the myocardium under low power and note that the muscle fibers are arranged in large bundles which pursue a spiral course in the ventricles. Study the pulmonary valve in slide 124. The valve is covered by endothelium.
Elastic fibers are present in the valve but most of the valve is made of dense collagenous tissue.
There are no blood vessels in a normal heart valve. Observe the attachment of the valve to the endocardium, which is thickened at that point. There are three different types of cardiac muscle fibers in the heart. Ordinary cardiac fibers are the principal type of cell in the myocardium. Their function is to contract the walls of the atria and ventricles.