How does your heart pump blood?

A pump you can feel

Put your hand flat on your chest, a little to the left of the middle. Can you feel a steady thump? That is your heart. It is about the size of your fist, and it is made of a special kind of muscle that keeps working all day and all night without ever getting tired.

Your heart is a pump. Its job is to push blood around your body. Blood carries oxygen and food to every part of you, from your brain to your toes, and it carries waste away. The heart does this without you ever having to think about it, even while you sleep.

When you are sitting still, a child's heart usually beats about 70 to 100 times a minute. Grown-ups' hearts are a little slower, around 60 to 100 beats a minute. Add it all up and your heart beats around 100,000 times a day. In less than a minute, it can send blood to every cell in your body.

Four rooms and four doors

Inside, the heart is divided into four hollow spaces called chambers. The two on top are the atria (one on its own is called an atrium). They collect blood as it arrives. The two on the bottom are the ventricles. They do the hard pushing. The left ventricle is the biggest and strongest chamber of all, because it has to push blood all the way around your body.

Between the chambers, and at the exits, are four valves. A valve is like a one-way door. It swings open to let blood through, then snaps shut so the blood cannot slide backwards. Look closely at the heart model in the photo: the white strings are the cords that hold the valve flaps in place.

When a doctor listens to your chest with a stethoscope, they hear "lub-dub, lub-dub". The "lub" is the sound of two valves closing. The "dub" is the other two closing a moment later. Your heartbeat is really the sound of doors shutting.

Two trips: to the lungs, then the body

Blood makes two trips through the heart. The right side collects blood coming back from the body. This blood is low on oxygen and is carrying carbon dioxide, a waste gas. The right ventricle pumps it the short way to the lungs. There the blood drops off the carbon dioxide, which you breathe out, and picks up fresh oxygen from the air you breathe in.

The oxygen-rich blood flows back to the left side of the heart. The left ventricle then pumps it out through the aorta, the biggest artery in your body, and off it goes to everywhere else.

Blood travels in tubes called blood vessels. Arteries carry blood away from the heart. Veins bring it back. Joining them are capillaries, tiny tubes that carry blood right up to your cells. The oxygen rides inside red blood cells, held by a protein called haemoglobin.

The spark that sets the beat

What tells the heart when to squeeze? A tiny cluster of cells in the right atrium, called the sinus node, sends out a small electrical signal. The signal spreads across the atria first, so they squeeze and push blood down into the ventricles. Then it reaches the ventricles, and they squeeze. Squeeze, squeeze, rest. That is one heartbeat.

The heart muscle needs its own supply of oxygen too. It gets it from the coronary arteries, which wrap around the outside of the heart like the branches of a tree.

An adult's heart weighs only about 300 to 450 grams, roughly as much as a full can of soft drink. Yet it keeps around 5 litres of blood moving around the body, every minute of every day.

Faster, slower, stronger

Your heart changes speed all the time. When you run, your muscles need more oxygen, so your heart beats faster to deliver it. Being excited or scared, or being sick with an infection, can also speed it up. When you rest, it slows down again.

You can feel each heartbeat as your pulse. Every beat sends a little wave along your arteries. Press two fingers gently on the thumb side of your wrist, or on the side of your neck next to your windpipe, and you will feel it tapping.

Like any muscle, the heart gets stronger with use. Australian health guidelines suggest kids run, swim, ride a bike or play sport for at least 60 minutes a day. That, plus plenty of fruit and vegetables, helps keep it healthy for a lifetime of thumping.

📚 Words to know

Atrium

One of the two top chambers of the heart, where blood arrives. Two of them are called atria.

Ventricle

One of the two bottom chambers of the heart. They do the strong pushing.

Valve

A one-way door inside the heart that stops blood from flowing backwards.

Artery

A blood vessel that carries blood away from the heart. The aorta is the biggest one.

Vein

A blood vessel that carries blood back to the heart.

Pulse

The beat you can feel in an artery each time your heart squeezes.

🧪 Try this: find your pulse and make it race

1. Sit still for a minute. Then press two fingers (not your thumb) gently on the thumb side of your wrist, just below the base of your hand, until you feel a steady tapping. That is your pulse.
2. Watch a clock or timer. Count the taps for 30 seconds, then double the number. That is your resting heart rate in beats per minute. Write it down.
3. Now do one minute of star jumps or running on the spot in a safe, open space. Straight away, find your pulse and count again. How much faster is it?
4. Sit down and count once more after two minutes, then after five. Watch your heart settle back towards normal as your muscles stop asking for extra oxygen.