The Heart by the Numbers

Your heart beats around 100,000 times a day. You can check that figure yourself. At about 70 beats a minute:

70 beats × 60 minutes × 24 hours = 100,800 beats a day

Keep that up for decades and the total becomes enormous: the Texas Heart Institute estimates that a heart may beat more than 3.5 billion times in a long lifetime. Unlike your arm or leg muscles, heart muscle never gets a long rest. It relaxes for a fraction of a second between beats and then contracts again.

Heart rate is the number of beats in a minute. For adults and children aged 10 and over, a resting rate of 60 to 100 beats per minute is normal. Younger children have faster hearts, according to the US National Library of Medicine:

Age	Normal resting rate (beats per minute)
Newborn (up to 1 month)	70–190
1–11 months	80–160
1–2 years	80–130
3–4 years	80–120
5–6 years	75–115
7–9 years	70–110
10 years and over, adults	60–100
Well-trained athletes	40–60

These are ranges for people at rest. Your own rate changes all day: it rises when you exercise, feel excited or nervous, and falls when you relax or sleep.

With each beat at rest, each ventricle pushes out about 70 millilitres of blood. This amount is called the stroke volume. The volume pumped by one ventricle in a minute is the cardiac output:

cardiac output = stroke volume × heart rate

For a resting adult: 70 mL × 75 beats a minute = 5,250 mL, or about 5.25 litres a minute. OpenStax gives this as the average, with a normal range of about 4 to 8 litres a minute.

Over a day that adds up to 5.25 litres × 1,440 minutes ≈ 7,560 litres. The Texas Heart Institute's figure is about 7,571 litres a day. An adult body holds only about 5 litres of blood in total, so at rest your whole blood supply passes through each side of the heart roughly once every minute.

A typical adult heart is about the size of a fist: roughly 12 cm long, 8 cm wide and 6 cm thick. It weighs about 250 to 300 grams in women and 300 to 350 grams in men, which matches the difference in average body size. A child's heart is smaller and grows with the rest of the body.

The wall of the left ventricle is the thickest part, because that chamber pushes blood all round the body.

The blood that leaves the heart travels through arteries, tiny capillaries and veins. According to the Texas Heart Institute, an adult's blood vessels laid end to end would stretch for more than 96,500 kilometres. The Earth's Equator is about 40,075 km long, so that is more than twice round the planet.