Cardiac muscle exists only within the heart of animals. It is a specialized form of muscle evolved to continuously and repeatedly contract, providing circulation of blood throughout the body. The heart is a relatively simple organ. Through all the twists and turns and various chambers, there are only three layers. The outer layer, known as the epicardium or visceral pericardium, surround the cardiac muscle on the exterior. This helps protect it from contact with other organs. The parietal pericardium attaches to this outer layer creates a fluid-filled layer which helps lubricate the heart. The inner layer, or endocardium, separates the muscle from the blood it is pumping within the chambers of the heart. In between these two sheets lies the cardiac muscle. Cardiac muscle is sometimes referred to as myocardium. This can be seen in the image below.