The heart is a cone-shaped muscle located in the mediastinum that pumps blood through the body. It has four chambers - two atria that receive blood and two ventricles that pump blood out. The heart contracts rhythmically through the cardiac cycle of diastole and systole. Blood flows through valves between the chambers and arteries during each phase. The heart is supplied with oxygenated blood from the coronary arteries to fuel its continuous pumping action.