Heart : Muscular pump with 4 chambers, contracting at regular intervals to force blood through the circulatory system.
Left side of heart receives & pumps oxygen rich blood from lungs to body. Right side of heart receives oxygen depleted blood from the body & pumps it to the lungs.

Left Atriu

Left Ventricle : Pumps oxygenated blood into the aorta & hence to all body cells (except lungs).

Septum : Thick wall that separates the left & right chambers of the heart.

Right Atrium : Receives oxygen poor blood from the body via the upper & lower vena cavas. Sends blood to right ventricle.

Right Ventricle : Pumps oxygen poor blood to the lungs.

Valve: Valves (like trap doors) between the atria and ventricles which allow flow into the ventricles, but no flow backwards to atria.

Atrio-ventricular Valves: The valves located between each atria and its adjoining ventrical. Closing of this valve during ventricular contraction prevents backblow of blood backwards into the atria.

Semilunar Valves: Valves in the pulmonary artery or aorta that close when the ventricle relaxes, preventing flow of blood from these large arteries back into the ventricles.

Pacemaker: (Sinoatrial node) Nerve tissues that receive impulses from brain or spinal column & transfer signal to heart. Controls heart beat. Found atop right atrium.

Vena Cava (superior & inferior): Large veins collecting oxygen poor blood from smaller veins in body. Superior v.c. brings blood from upper body, inferior v.c. brings blood from the lower body.

Aorta : Large, thick muscled artery through which oxygenated blood leaves the heart (from left ventricle) for the body tissues.

Pulmonary Artery : Artery transporting oxygen poor blood from right ventricle to lungs.

Pulmonary Vein : Vein transporting oxygen rich blood from lungs to left atrium.

Artery : Transports blood outward from heart to all body tissues. Must be thick, muscular & elastic to withstand pressure from heartbeat.

Capillary : Thin blood vessels in the tissues (about one red blood cell wide) through which oxygen & nutrients diffuse to the cells, and wastes & CO2 diffuse into the blood. Found between all arteries & veins.

Vein : Blood vessels carrying blood towards the heart from body tissues or organs. Are thin-walled as blood pressure is low.

Includes right ventricle--->pulmonary artery--->lungs---> pulmonary vein--->left atrium. Involves oxygenation of blood!