A pump squeezing
What Is a Heartbeat?
Your heart is a muscle squeezing blood around a loop, about once a second, for life.
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Step 1 of 5
Every cell needs a delivery.
Cells need oxygen and fuel constantly and cannot fetch their own. Blood is the delivery system, and it has to keep moving.
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Step 2 of 5
The heart is a muscle, not a machine part.
It is a hollow muscle that squeezes. Each squeeze forces blood out; each relaxation lets it refill. That cycle is one beat.
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It is really two pumps side by side.
The right side sends blood to the lungs for oxygen. The left side sends the oxygen-rich blood to the rest of the body.
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Valves stop it flowing backwards.
Flaps snap shut after each squeeze so blood can only go one way. Those closing valves are the lub-dub you hear.
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Step 5 of 5
It speeds up when you need more.
Running muscles demand more oxygen, so the rate climbs. Resting, it drops. It is matching supply to demand, continuously.
Your heart beats around 100,000 times a day and roughly three billion times in a lifetime, without maintenance.
The short version
A heartbeat is a muscle squeezing blood around a one-way loop, and the sound is its valves snapping shut.
Try it yourself
Find your pulse, count for 15 seconds and multiply by four. Then run up stairs and do it again.
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