Blood Flow & Circulatory System Simulator
Follow blood from the heart through arteries, arterioles, capillaries and veins, and see how strongly flow depends on vessel radius.
Follow blood from the heart through arteries, arterioles, capillaries and veins. Change the arteriole radius and see how strongly flow depends on it - and watch the pressure fall along the tree.
About the Blood Flow & Circulatory System Simulator
Free blood flow & circulatory system simulator. Follow blood from the heart through arteries, arterioles, capillaries and veins, and see how strongly flow depends on vessel radius. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for biology, the blood flow & circulatory system simulator runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Follow blood from the heart through arteries, arterioles, capillaries and veins, and see how strongly flow depends on vessel radius. Use it to explore biology ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Blood Flow & Circulatory System Simulator
- Use the controls to change Arteriole radius, Blood viscosity, Driving pressure (heart), Heart rate. The simulation reacts instantly.
- Press "Check flow drop", "Check compensation", "Reset to defaults", "📄 Lab Report" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Halve the arteriole radius and predict the drop in flow before checking.
- Raise blood viscosity and compare it with the effect of the same percentage change in radius.
- Read the pressure-along-the-tree graph and find where pressure falls fastest.
Key ideas you can learn
- Poiseuille's law: flow is proportional to the fourth power of the vessel radius.
- Arterioles are the body's main resistance vessels because their radius changes the most.
- Blood pressure falls steadily along the vascular tree, dropping fastest across the arterioles.
- Higher blood viscosity or lower driving pressure both reduce flow.
Where this is used in the real world
This r⁴ relationship is why blood-pressure medications that dilate arterioles work so powerfully, and why cholesterol plaques that narrow arteries are so dangerous.
Who is this simulation for?
Biology students and teachers who want to explore living systems, populations and genetics interactively and safely.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why does a small change in blood vessel radius change flow so much?
Because flow depends on radius to the fourth power, so halving the radius cuts flow to about one sixteenth.
Where does blood pressure fall the most in the circulatory system?
Across the arterioles, which is exactly why the body uses them to control blood pressure and how much blood organs receive.
Is the Blood Flow & Circulatory System Simulator free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Blood Flow & Circulatory System Simulator work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.