the human heart quick facts
- Your heart is about the size of your fist.
- It beats around 100,000 times a day.
- It has four chambers and four valves.
- The lub-dub sound is made by valves closing.
- Your blood vessels would stretch about 96,500 km end to end.
What does the heart do?
Your heart is a strong, hard-working muscle that pumps blood all around your body. The blood carries oxygen and food to every part of you, from your brain to your toes.
It never takes a break. The British Heart Foundation says your heart beats around 100,000 times a day, keeping about 5 litres (8 pints) of blood moving around your body.
The heart is the centre of your circulatory system, the network of blood vessels that carries blood everywhere. Learn more about the whole network in our circulatory system facts.
| Your heart at a glance | |
|---|---|
| Size | about as big as your fist |
| Where | in your chest, near the middle, tilted a little to the left |
| Chambers | 4: two atria and two ventricles |
| Valves | 4: tricuspid, pulmonary, mitral and aortic |
| Beats a day | about 100,000 |
| Blood pumped a day | about 7,571 litres (2,000 gallons) |
| Resting rate, ages 10 and up | 60 to 100 beats a minute |
Where is your heart?
Many people think the heart is on the far left side of the chest. In fact, the Cleveland Clinic says it sits behind and slightly to the left of your breastbone, between your two lungs.
Your rib cage wraps around it like a helmet, protecting it from bumps and knocks.
Try this: put your hand flat on the middle of your chest, a little to the left. When you are still and quiet, you may be able to feel your heart beating.
How big is your heart?
The British Heart Foundation says your heart is roughly the size of your fist. As you grow, your heart grows with you.
An adult heart weighs about 280 g (10 ounces) on average, the Cleveland Clinic says. The Texas Heart Institute gives a range of about 200 to 425 g, because heart size depends on how big a person is.
Four rooms inside
Inside, your heart is divided into four hollow spaces called chambers. The two top chambers are called atria. The two bottom chambers are called ventricles.
The British Heart Foundation explains that the atria collect blood coming into the heart, and the ventricles pump blood out. A muscular wall called the septum runs down the middle, keeping the left side separate from the right side.
The left ventricle has the hardest job, pushing blood all the way around your body. The Texas Heart Institute says its wall is only about 1.3 cm (half an inch) thick, yet it is strong enough to do that with every beat.
The heart wall itself has three layers, the Cleveland Clinic says: a smooth inner lining, a thick middle layer of muscle and a thin outer layer.
Four one-way doors
Your heart has four valves. The British Heart Foundation and the Cleveland Clinic say they work like one-way doors, opening to let blood through and then snapping shut so it cannot flow backwards.
Their names are the tricuspid valve, the pulmonary valve, the mitral valve and the aortic valve. The tricuspid valve sits between the two right chambers, and the mitral valve sits between the two left chambers.
Lub-dub: the sound of your heart
If a doctor listens to your chest with a stethoscope, they hear a sound like “lub-dub, lub-dub”. That sound is made by the valves closing.
The US National Heart, Lung, and Blood Institute (NHLBI) says the “lub” is the valves between the atria and ventricles closing. The “dub” is the aortic and pulmonary valves closing a moment later.
The journey of your blood
Blood follows the same path through your heart every time. The NHLBI describes it step by step.
First, blood that has used up its oxygen comes back from your body. It enters the right atrium through two big veins called the vena cava.
Next, it passes through the tricuspid valve into the right ventricle. The right ventricle pumps it through the pulmonary valve and along the pulmonary artery to your lungs.
In the lungs, the blood picks up fresh oxygen. The oxygen-rich blood then flows back to the heart through the pulmonary veins and into the left atrium.
Finally, it moves through the mitral valve into the left ventricle. The left ventricle squeezes hard, sending the blood through the aortic valve into the aorta, the body’s biggest artery, and out to the rest of your body.
So the right side of your heart pumps blood to your lungs, and the left side pumps blood to everywhere else.
Feeding the heart itself
Your heart is a muscle, so it needs oxygen too. The NHLBI says the heart has its own blood vessels, called coronary arteries, that wrap around it and bring it oxygen-rich blood.
Coronary veins then carry that blood back to the right atrium, ready to start the journey again.
Your blood vessels
Blood travels through tubes called blood vessels. Arteries carry blood away from the heart. Veins carry blood back to it.
The smallest blood vessels are called capillaries. The Cleveland Clinic says their walls are so thin that oxygen and food can pass out into your body, while waste such as carbon dioxide passes in.
Your body has an enormous number of blood vessels. The Cleveland Clinic and the Texas Heart Institute say that, laid end to end, they would stretch about 96,500 km (60,000 miles). That is enough to go around the Earth more than twice.
The Cleveland Clinic says people have about 160 named arteries and 200 named veins, but most of the body’s billions of blood vessels are tiny capillaries.
The heart’s electrical system
What makes your heart beat? It has its own built-in electrical system. The NHLBI says it controls how fast and how steadily your heart beats.
Each beat starts in a small group of special cells in the right atrium, called the sinoatrial node, or SA node. The British Heart Foundation calls it the heart’s natural pacemaker.
The signal spreads across the atria, making them squeeze. Then it reaches the atrioventricular node, or AV node, where it slows down for a moment. After that, the Cleveland Clinic says, it races down special pathways to the ventricles, making them squeeze too.
Your heart is not the only organ with electrical signals. Find out how your body’s control centre works in our brain facts.
Heart numbers
Your heart does an incredible amount of work. The Texas Heart Institute says an average heart pumps about 7,571 litres (2,000 gallons) of blood in a single day.
Over a long life, it says, a heart may beat more than 3.5 billion times.
Heart rate
Your heart rate is how many times your heart beats in one minute. It is usually faster in young children and slower in adults. MedlinePlus, from the US National Library of Medicine, gives these normal resting rates.
| Age | Normal resting heart rate (beats a minute) |
|---|---|
| Newborn babies | 70 to 190 |
| 1 to 11 months | 80 to 160 |
| 1 to 2 years | 80 to 130 |
| 3 to 4 years | 80 to 120 |
| 5 to 6 years | 75 to 115 |
| 7 to 9 years | 70 to 110 |
| 10 years and older, and adults | 60 to 100 |
| Well-trained athletes | 40 to 60 |
Many things can make your heart beat faster. Exercise does, because your muscles need more oxygen. The British Heart Foundation says a fever, feeling worried, not drinking enough water and some medicines can speed it up too.
How to take your pulse
Each time your heart beats, it sends a push of blood through your arteries. You can feel this push, called your pulse, in places where an artery is close to your skin.
MedlinePlus says to place the tips of your first two fingers on the inside of your wrist, just below the base of your thumb. Press gently until you feel a beat.
Count the beats for 30 seconds, then double the number. For a true resting rate, sit quietly for at least 10 minutes first.
Safety tip: MedlinePlus warns never to press on both sides of your neck at the same time, because that can reduce the blood flowing to your head.
Keeping your heart healthy
Your heart is a muscle, and like other muscles it gets stronger when you use it. The US Centers for Disease Control and Prevention (CDC) says children and teenagers aged 6 to 17 should be active for 60 minutes or more every day.
The CDC says that should include hard exercise, such as running, on at least three days a week. It also recommends activities that build muscles, like climbing, and activities that build bones, like jumping, each on at least three days a week.
Tell a trusted adult if your heart often feels very fast, very slow or uneven, or if you feel dizzy or faint. The British Heart Foundation says those are signs to see a doctor.
Three things people get wrong
Your heart is not on the far left of your chest. It sits near the middle, tilted a little to the left.
Not all arteries carry oxygen-rich blood. The pulmonary artery carries oxygen-poor blood to the lungs.
Your heart does not pump just 5 litres a day. That is the blood it keeps moving; it pumps thousands of litres a day.
Did you know? Laid end to end, your blood vessels would stretch around the Earth more than twice.
Try it
Take your pulse at your wrist for 30 seconds and double it. Then do 20 star jumps and take it again. What changed?
Knowledge check
Which side of the heart pumps blood to the lungs?
Show answer
The right side.
What makes the lub-dub sound?
Show answer
The heart’s valves closing.
Frequently asked questions
How big is the human heart?
It is about the size of your fist. An adult heart weighs about 280 g on average, and it grows as you grow.
Where is the heart?
It sits in your chest behind and slightly left of your breastbone, between your two lungs, protected by your rib cage.
How many chambers does the heart have?
Four: two upper chambers called atria that receive blood, and two lower chambers called ventricles that pump it out.
What is a normal heart rate for a child?
MedlinePlus gives 70 to 110 beats a minute at rest for ages 7 to 9, and 60 to 100 for ages 10 and older.
What makes the heart beat?
A built-in electrical system. Each beat starts in the SA node, the heart’s natural pacemaker, in the right atrium.
How can I keep my heart healthy?
The CDC says children aged 6 to 17 should be active for 60 minutes or more every day, including running, climbing and jumping.
Sources
- NHLBI (US National Institutes of Health): how blood flows through the heart — the path of blood, the valves and the coronary arteries; its page on how the heart beats was also used
- Cleveland Clinic: the heart — location, weight, chambers, wall layers and the electrical pathways; its blood vessels page was also used
- British Heart Foundation: how a healthy heart works — beats a day, blood volume, chambers, valves and the pacemaker; its heart rate page was also used
- MedlinePlus (US National Library of Medicine): pulse — resting heart rates by age and how to take a pulse safely
- Texas Heart Institute: heart anatomy — weight range, blood pumped a day, lifetime beats, vessel length and the left ventricle wall
- US CDC: physical activity for children — daily activity guidance for ages 6 to 17
