Just for a second, place your hand over your heart and feel it thumping. The heart is the body’s engine room, beating continuously as it pumps blood around the body. This remarkable organ is a true lifelong friend – all it asks in return is nutritious blood to pump around your body. Situated left centre of the chest, the heart is about the size of a clenched fist and weighs around 250g/8oz. As long as it is supplied with oxygen and nutrients it will go on contracting, spontaneously, rhythmically and completely automatically.
As you’re reading this, it’s beating between 50 and 90 times a minute, depending on your age, its condition and your level of fitness. During strenuous exercise, however, this may increase to about 180-200 beats a minute.
The heart is really two pumps. One receives oxygenated blood from the lungs and pumps it around the body. The blood leaves the heart through the aorta (which is the biggest artery in the body) and is distributed to all organs, tissues and cells through a succession of increasingly small tube-ways (capillaries). Compared to the width of the aorta (1cm), capillaries are tiny, barely half a millimetre across. Having delivered its oxygen and nutrients – and picking up carbon dioxide and waste products on the way back – blood returns to the heart via a system of veins.
The other pump receives de-oxygenated blood from the body and sends it to the lungs where carbon dioxide is exchanged for more oxygen. This complex network of arteries, veins, blood vessels and capillaries carry blood to and from the body in a continuous figure of eight circuit. Beating around 40 million times a year, each beat pumps around 0.15 litres (0.25 pints) of blood in and out of the heart – a staggering 9100 litres (2000 gallons) a day, or 227 million litres (50 million gallons) in a lifetime.
How your heart age is key to heart attack or stroke risk | BBC | 4 Sep 2018
The heart test: how healthy is your heart? | NHS
How the heart the works | BUPA | 15 Aug 2013 | 3m03s