Anatomy of the human heart

Heart chambers

The heart is divided into four chambers:

• right atrium
• right ventricle
• left atrium
• left ventricle

The right and left sides of the heart are separated by a muscular wall known as the septum.

The septum protects oxygen-rich blood from mixing with oxygen-poor blood.

Heart valves

The heart has four valves that keep blood moving in the correct direction by only opening one way.

These valves are the:

• tricuspid valve
• mitral valve
• pulmonary valve
• aortic valve

Each valve has flaps, called leaflets or cusps, that open and close once during each heartbeat.

Coronary circulation

Oxygen-poor blood travels to the heart from everywhere in the body, except the lungs.

This blood enters the right atrium and then flows to the right ventricle. From there it is pumped to the lungs through the pulmonary arteries.

The lungs refresh the blood with a new supply of oxygen, which comes from the air we breathe. The lungs also remove carbon dioxide from the blood, which is then removed from the body through the air we breathe out.

Oxygen-rich blood returns from the lungs and enters the left atrium and then flows to the left ventricle. From there it is pumped through the main artery that supplies blood to the entire body, called the aorta, to supply tissues throughout the body with oxygen.

The heart muscle itself also receives oxygen-rich blood via the coronary arteries that extend over the surface of the heart.

Heart conduction system

A beating heart contracts and relaxes. Contraction is called systole and relaxation is called diastole.

During systole, the ventricles contract, forcing blood into the vessels going to the lungs and body.

During diastole, the ventricles relax, allowing them to fill with blood from the upper chambers aka the left and right atria.

This cycle is driven by the heart's electrical wiring, called the conduction system. Electrical impulses begin high in the right atrium, in the sinus node, and travel through specialised pathways to the ventricles, delivering the signal for the heart to pump.

This conduction system keeps the heart beating in a coordinated and normal rhythm, which in turn keeps blood circulating. This results in the continuous exchange of oxygen-rich blood with oxygen-poor blood that is necessary to keep the body working.

Facts about the heart

• the heart beats around 100,000 times a day and around 2.5 billion times during an average lifetime
• a woman’s heart beats an average of eight beats more per minute than a man’s heart
• the sounds of a heartbeat are caused by the closing of the heart valves
• the heart provides blood to every part of the body except for the cornea, which is the outer layer of the eye and needs to remain transparent to refract light
• the blood vessels in an adult are around 100,000 kms long in total
• the average adult has approximately five litres of circulating blood
• research has shown that deadly heart attacks are more likely to occur on a Monday