The heart is composed of three distinct layers: the thin endocardium, the thick myocardium, and the outer epicardium, which connects it to the thoracic cavity. Surrounding the heart is a protective double membrane sac known as the pericardium. With four chambers—two atria and two ventricles—the human heart plays a crucial role in the circulatory system, which varies across different organisms but is primarily focused on mammals in this discussion.
