The document describes the main functions and components of the cardiovascular system. It explains that the heart is located in the chest cavity and surrounded by membranes. It has four chambers - two atria and two ventricles - and valves that allow blood to flow in only one direction. The heart pumps oxygenated blood through the arteries and deoxygenated blood through the veins in a continuous cycle to supply all parts of the body with nutrients and oxygen and remove waste.