How do we know?
↻ One of the pages with a moving picture
A doctor rolled up a sheet of paper and listened.
- With each heartbeat, an electrical signal travels from the top of the heart to the bottom.
- The signal makes the heart muscle squeeze, pushing blood out to your whole body. Then it relaxes and fills again.
- Your heart has four chambers: two on each side, a top one and a bottom one.
- Four valves work like one-way doors. When they snap shut you hear “lub-DUB”!
In 1816 in Paris, a doctor named René Laennec rolled a sheet of paper into a tube to listen to a heart. He was surprised: through the paper tube he could hear the heart far more clearly than with his ear on the chest.
His idea became the stethoscope that doctors use today.
Make a fist: that’s roughly how big your heart is. It sits only a little to the left of the middle of your chest.
Wow number
100,000 The average heart beats about 100,000 times a day!
Myth or fact?
Your heart is on the far left side of your chest. Myth. It sits only a little to the left of the middle of your chest.
Your heart is about the size of your fist. Fact. Make a fist: that’s roughly how big your heart is.
Think about it
Why do you think your heart beats faster when you run?
Where in the world?
Paris, France where, in 1816, a doctor named René Laennec rolled a sheet of paper into a tube to listen to a heart — 48.8566° N, 2.3522° E.
Where these facts come from
Every number on page 71, and who measured it
This page tells us how the heart pumps blood and how big it is.
Heart & Circulatory System — KidsHealth, a health site for kids from Nemours Children's Health
kidshealth.org/en/kids/heart.html
We checked it on 31 October 2026
This page tells us how the heart's valves keep blood flowing the right way.
How the Heart Works — The U.S. National Heart, Lung, and Blood Institute
nhlbi.nih.gov/health/heart
We checked it on 31 October 2026
This page tells us where the heart sits in your chest.
Heart Anatomy — The Texas Heart Institute, a heart hospital and research center in Houston
texasheart.org/heart-health/heart-information-center/topics/heart-anatomy
We checked it on 31 October 2026
This page tells us how Laennec rolled up paper to make the first stethoscope in Paris in 1816.
Rene Theophile Hyacinthe Laënnec (1781–1826): The Man Behind the Stethoscope — A history article about Laennec, the doctor who invented the stethoscope, shared by the U.S. National Library of Medicine
pmc.ncbi.nlm.nih.gov/articles/PMC1570491
We checked it on 31 October 2026
Has this changed?
How the heart beats is not going to change.
What does change is your own heart rate: it goes up when you run and down when you rest.
Words from this page
- chamber
- A hollow room in the heart that fills with blood. The heart has four.
- valve
- A one-way door in the heart that keeps blood flowing the right way.
- stethoscope
- A tool doctors use to listen to the heart.
Try it!
Make a paper-tube stethoscope.
1. Roll a sheet of paper into a tube and tape it. 2. Hold one end gently on a friend’s chest, a little left of the middle. 3. Put your ear to the other end. Then try again after your friend hops 20 times.
What happens: you can hear “lub-DUB”, and it gets faster after hopping.
Go further