Heart

A muscular organ that pumps blood through the body, a human heart is about the size of a fist.

The flow of blood into and out of the heart:

Oxygen-poor blood enters the right atrium of the heart via veins called the inferior vena cava and the superior vena cava.
The blood is then pumped into the right ventricle and then through the pulmonary artery to the lungs, where the blood is enriched with oxygen and loses carbon dioxide.
Oxygenated blood is then carried back to the left atrium of the heart via the pulmonary vein.
Blood is then pumped to the left ventricle.
Blood is pumped through the aorta and to the rest of the body.

This cycle is then repeated.

Every day, the heart pumps about 7,600 litres of blood, and beats around 100,000 times.

Aorta

A blood vessel carrying blood away from the heart.

Inferior vena cava

a blood vessel carrying blood to the heart.

Left atrium

the left upper chamber of the heart. It receives oxygen-rich blood from the lungs via the pulmonary vein.

Left ventricle

the left lower chamber of the heart. It pumps the blood through the aortic valve into the aorta.

Mitral valve

the valve between the left atrium and the left ventricle. It prevents the back-flow of blood from the ventricle to the atrium.

Pulmonary artery

The blood vessel that carries oxygen-poor blood from the right ventricle of the heart to the lungs.

Pulmonary valve

the flaps between the right ventricle and the pulmonary artery. When the ventricle contracts, the valve opens, causing blood to rush into the pulmonary artery. When the ventricle relaxes, the valves close, preventing the back-flow of blood from the pulmonary artery to the right atrium.

Pulmonary vein

The blood vessel that carries oxygen-rich blood from the lungs to the left atrium of the heart.

Right atrium

The right upper chamber of the heart. It receives oxygen-poor blood from the body through the inferior vena cava and the superior vena cava.

Right ventricle

The right lower chamber of the heart. It pumps the blood into the pulmonary artery.

Septum

the muscular wall that separates the left and right sides of the heart.

Superior vena cava

A large vein that carries oxygen-poor blood to the right atrium from the upper parts of the body.

Tricuspid valve

the flaps between the right atrium and the right ventricle. It is composed of three leaf-like parts and prevents the back-flow of blood from the ventricle to the atrium.