What it does
Your blood makes two trips for every one round your body. The right side of the heart pumps oxygen-poor blood to the lungs; it comes back rich in oxygen to the left side, which pumps it out to the whole body. That is double circulation. This page shows it as a loop of moving blood cells: red where the blood is rich in oxygen, blue where it is low in oxygen, and purple where the two mix. One cell has a dark ring, and the list under the picture shows where it is right now. Switch to a frog (three chambers, so the blood mixes in its one ventricle) or a fish (two chambers, single circulation through the gills) to see why mammals and birds need four chambers. To slow down a single heartbeat and see the valves, open the cardiac cycle; to see how haemoglobin picks up and drops oxygen on the way, try the oxygen dissociation curve; and for where the food in the blood comes from, the digestion journey.
Using it
- Pick an animal: human, frog or fish.
- Move the heart rate (beats a minute) and stroke volume (mL pushed out by each ventricle per beat). The cells speed up or slow down.
- Read the numbers: cardiac output, the time for the blood to go round once, the laps in a day and the litres pumped in a day.
- Follow the ringed cell and read one trip round the body, step by step.
- Pick Class 11 for the names of the valves and vessels in the picture and a note on the pulmonary artery and veins.
The picture runs ten times faster than real life, so one lap takes about 6 seconds on screen instead of about a minute.
Worked example
At rest, a heart beating 75 times a minute that pushes out 70 mL a beat has a cardiac output of 75 × 70 = 5250 mL a minute, or 5.25 L a minute. An adult has about 5 L of blood, so it goes round once in about 5 ÷ 5.25 = 0.95 minutes, which is about 57 seconds. In a day the heart pumps about 7560 L, and the blood goes round about 1512 times. Push the heart rate to 150 and the output doubles to 10.5 L a minute, so one lap takes about 29 seconds.
Where this fits in school
Class 10 science (life processes) covers the human heart, why the oxygen-rich and oxygen-poor blood must be kept apart, double circulation, and the hearts of fish and amphibians. Class 11 biology (body fluids and circulation) adds the valves, the cardiac cycle and cardiac output. This page is an independent learning aid. It is not made by or connected with NCERT, and it does not copy any textbook.
Questions
Is blood really blue? No. Oxygen-poor blood is a darker red. Blue is the usual colour in diagrams to tell the two apart.
Why is the left ventricle wall thicker? It pumps blood round the whole body, which needs a much higher pressure than the short trip to the lungs.
Are these my numbers? No. They are typical round values for a resting adult, for teaching. This is not a medical tool.
Is anything saved? No. Nothing you enter is stored or sent anywhere.
Where the numbers come from
- The route of blood in fish, amphibians and mammals and the parts of the heart: standard school biology, written by fibub in its own words.
- Typical round adult values (about 5 L of blood, 70 mL stroke volume, 75 beats a minute at rest) are rounded teaching figures, not medical data.
- Cardiac output = heart rate × stroke volume and lap time = blood volume ÷ cardiac output, checked by hand in the tests.
- Drawings are fibub's own simple shapes. Nothing you enter is stored or sent anywhere.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.