Simple illustration of the human heart

The Human Heart

Anatomy of the human heart

The heart is a muscular organ that pumps blood throughout the body. This blood provides the body with oxygen and nutrients while also removing waste products, such as carbon dioxide.

The heart is about the size of a fist and is located in the middle of the chest, just to the left of the breastbone (sternum).

Together, the heart and blood vessels make up the cardiovascular system.

Heart chambers

The heart is divided into four chambers:

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:

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.

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Acknowledgement of Country

The Victor Chang Cardiac Research Institute acknowledges Traditional Owners of Country throughout Australia and recognises the continuing connection to lands, waters and communities. We pay our respect to Aboriginal and Torres Strait Islander cultures; and to Elders past and present.

Victor Chang Cardiac Research Institute - The Home of Heart Research for 30 Years