human heart diagram

Your heart is an amazing organ:

It is the powerhouse of your body; the engine that drives blood to all parts.

It is a massively strong muscle, yet weighs only about 340g or 12 ounces, and is about the size of a clenched fist.

It never rests for more than a second and beats tirelessly and efficiently.

It is far more durable than any man-made pump and its moving parts are almost indestructible.

It is one of the few organs we can actually feel working and the heart has become synonymous with the very spirit of life itself - love, excitement, fear and courage.

A strong and efficient heart is one of the secrets of a long and healthy life.

More incredible facts about your heart

It beats on average 100,000 times a day, that's more than once a second.
It pumps out between 6 and 50 litres of blood every minute.^*
On a typical day it pumps more than 9,000 litres of blood.
In a typical year it pumps 4.5 million litres of blood.
In a typical lifetime it will beat up to 3,000 million times.
And will pump 250 million litres of blood.

^*If you are sitting down or are inactive, your heart will beat about 60-80 times a minute and pump out around 80 millilitres (ml) of blood with each stroke - around 6 litres a minute. However, if you are exercising, your heart rate can rise to an astounding 200 beats per minute and the output of blood can increase to 250 ml per beat - as much as 50 litres a minute.

What your heart does

The heart's job is to pump blood, which carries oxygen and nutrients, round the body to every organ and muscle to supply them with oxygen and nutrients, so that the body can work. After oxygen and nutrients have been delivered to the cells, the blood containing unwanted carbon dioxide and other waste materials is carried back to the heart. The heart lies across the middle of the chest between the lungs and is a hollow muscular double pump consisting of four chambers.

Grand tour of the heart

The four chambers are called the right and left atria, and right and left ventricles. Blood returning from the body in the (blue) veins, low in oxygen and high in carbon dioxide, collects in the right atrium and is pumped into the right ventricle.

Each time the right ventricle contracts, it propels blood into the lungs to be enriched with oxygen. Freshly oxygenated blood is then sent back from the lungs to the left atrium, which in turn contracts and sends it to the left ventricle. This is the heart's main pumping chamber and from here blood circulates the body through the system of arteries (red).

Four valves control the blood flow in the heart, each opens to let the blood through when the chambers contract and then snaps shut to prevent blood flowing back when they relax. The heartbeat sound comes from the opening and closing of these valves.

The cardiac cycle is a ceaseless two-phase rhythm of contraction (the systolic phase) and relaxation (the diastolic phase) stimulated and regulated by tiny electrical currents, each equivalent to a millionth of the current in a 100 watt light bulb. The muscular walls of the atria and ventricles, known as the myocardium, continuously produce these.

The whole cycle takes less than a second, so there are some 70 beats a minute when the body is at rest and up to 200 or more during extreme exercise. The fitter you are, the slower your heart rate. Some athletes have a pulse rate of only 35 beats a minute.

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