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Your heart beats about 100,000 times a day. How does a squeeze become blood pressure?
Heart & Circulation lab · Last updated: 16 October 2026
Your heart beats about 100,000 times a day. In this 3D lab, you watch the chambers fill and squeeze, follow blood to the lungs and body, and see how a squeeze becomes blood pressure. It makes sense of a pulse, a doctor's blood pressure reading and why exercise makes the heart race.
What you'll discover
- The heart is two pumps side by side: the right sends blood to the lungs and the left sends it to the body.
- Valves stop blood flowing backwards, and their closing makes the 'lub-dub' sound of a heartbeat.
- Blood pressure is highest as the ventricles squeeze and lowest as they relax, giving two numbers.
The science in plain words
The heart is a muscular pump about the size of a fist, with four chambers. The two upper chambers, the atria, receive blood returning from the body and lungs. The two lower chambers, the ventricles, pump it out. The right side sends oxygen-poor blood to the lungs to pick up oxygen, and the left side sends oxygen-rich blood to the rest of the body. This double circulation keeps the two kinds of blood apart.
Each beat begins with an electrical signal from a natural pacemaker in the heart wall. The atria contract first, then the ventricles squeeze hard and push blood into the arteries. Valves between the chambers and at the exits snap shut to stop blood flowing backwards, and that closing produces the 'lub-dub' a doctor hears through a stethoscope.
When the ventricles squeeze, they force blood into elastic arteries, raising the pressure; when they relax, the pressure falls but does not drop to zero. That is why blood pressure has two numbers, such as 120 over 80, a typical healthy adult reading measured in millimetres of mercury. At rest an adult heart pumps around 5 litres of blood a minute, roughly the whole blood supply. During exercise, the heart beats faster and harder to deliver extra oxygen to working muscles.
Where it fits
- India, NCERT: Class 10 science, Chapter 5: Life Processes
- United States: Grades 6 to 12
- Next Generation Science Standards: MS-LS1-3, HS-LS1-2
Common questions
How many times does the heart beat in a day?
At a typical resting rate of around 70 beats a minute, the heart beats about 100,000 times a day. Children's hearts usually beat faster than adults', and any heart speeds up during exercise, excitement or fever.
What do the two blood pressure numbers mean?
The top number is the pressure in the arteries when the heart squeezes, and the bottom number is the pressure when it relaxes between beats. A reading of about 120 over 80 is typical for a healthy adult. Doctors measure it in millimetres of mercury.
Why does the heart make a lub-dub sound?
The sound comes from the heart's valves closing. The 'lub' is the valves between the upper and lower chambers shutting as the ventricles start to squeeze. The 'dub' is the valves at the exits to the arteries shutting as the ventricles relax.
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Try it yourself
The Heart & Circulation lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.