Heart
Pumps blood through two separate circuits: the right side sends blood to the lungs to collect oxygen, the left side sends it to the rest of the body. The two sides beat together but work at very different pressures, which is why the left ventricle wall is roughly three times thicker.
Where it is
Centre of the chest, tilted slightly left, between the lungs and behind the sternum.
The numbers
- Mass
- 250–350 g
- Resting rate
- 60–100 beats per minute
- Output at rest
- about 5 litres per minute
- Beats per day
- roughly 100,000
Worth knowing
The heart has its own pacemaker — the sinoatrial node — and will keep beating outside the body given oxygen and nutrients, which is what makes transplantation possible. Cardiac muscle is unique in being both involuntary and striated, and it cannot be tetanised: it is physically incapable of the sustained contraction that would stop it refilling.
A common claim that is wrong
The heart is not on the left. It sits near the centre, angled so the apex points left, which is why the beat is felt there.
Structural reference only — this is not medical advice, and individual variation in every figure here is substantial. Anything concerning your own health belongs with a clinician rather than a reference page.
Common questions
- What does the heart do?
- Pumps blood through two separate circuits: the right side sends blood to the lungs to collect oxygen, the left side sends it to the rest of the body.
- Heart — key numbers
- Mass: 250–350 g. Resting rate: 60–100 beats per minute. Output at rest: about 5 litres per minute. Beats per day: roughly 100,000.
- Is it true that…
- The heart is not on the left. It sits near the centre, angled so the apex points left, which is why the beat is felt there.
Related pages
- Brain About 1.4 kg, using roughly 20% of the body’s energy at 2% of its mass.
- Liver The largest internal organ, around 1.5 kg, and the only one that regenerates.
- Lungs Two unequal lungs with a gas-exchange surface of about 70 square metres.
- Skin The largest organ — about 2 m² and 4 kg in an adult.
- Kidneys Two fist-sized filters processing about 180 litres of blood a day.
- Bones Bones
- Blood types Blood
- Teeth Teeth
- Blood Blood
- The senses Senses
- Taste Senses
Sources
- Typical range compiled from manufacturer specifications — At One Place