Blood Circulation
Change the heart rate and calculate how much the heart pumps in a minute. Follow one red drop: fast in the aorta, very slow in the capillaries. See why it slows down, too.
A simplified teaching model. This is not medical advice.
The heart and its two loops
Now in: Aorta oxygen-rich blood
The thick vessel leaving the left ventricle. The way through is narrow, so the flow is fast.
Typical speed: 20-40 cm/s Sources give a range of values.
Motion on screen is compressed for viewing (the real difference is much bigger).
How much the heart pumps (calculation)
About 70 mL is typical; sources give roughly 60 to 100 mL. At rest, about 60 to 100 beats per minute is one common reference range. This model makes no judgement.
Calculation
70 mL x 70 beats/min = 4,900 mL/min (= 4.9 L/min)
Time for one trip (calculated estimate)
5,000 mL / 4,900 mL/min = about 61 s
Blood volume divided by the amount pumped per minute, an average estimate. Real trips differ by route, and this is not a measured value.
Why so slow in the capillaries?
The amount of blood flowing is the same everywhere, so speed x cross-section stays constant. Each capillary is thin, but all of them together have a cross-section about 900 to 2,000 times the aorta (calculated from the sources' areas). The flow slows by the same factor.
Heartbeats so far (calculation)
Calculation
Per day: 70 x 60 x 24 = 100,800
Total: 100,800 x 365 x 40 = 1,471,680,000
about 1.5 billion beats
This assumes the heart rate never changes. In reality it varies with activity, sleep and age, so treat it as a rough figure.
Do blood vessels really stretch 2.5 times around the Earth?
The familiar claim of "about 100,000 km, 2.5 times around the Earth" has not been confirmed as fact. It traces back to a calculation in a book from around 1922 that assumed a 50 kg muscle mass and a very dense capillary network, and counted only muscle capillaries. Later research suggests those assumptions are much higher than modern measurements, so current estimates are much shorter. The true length is not known. Try the calculator below to see how changing assumptions changes the answer many times over.
Result for these assumptions (muscle only)
about 6,900 km
This is a calculation from assumptions, not the real length.
A simplified teaching model. This is not medical advice.
How to play
Press "Run it for me" and the red drop leaves the heart, travels around the body and the lungs. You can stop it and move it with the position slider or the place buttons. Further down, change the heart rate to see how much the heart pumps per minute, and enter an age and heart rate for a rough total of heartbeats.
Learn more
The right side of the heart sends blood returning from the body on to the lungs (the lung circuit), and the left side sends oxygenated blood from the lungs out to the body (the body circuit). Both sides pump the same amount, so blood traces a figure eight. At about 70 mL per beat (sources say 60 to 100 mL) and 70 beats a minute, the heart pumps about 5 L per minute. That is close to the blood in the body (about 5 L for a 70 kg person, roughly 7 to 8% of body weight), so dividing gives a calculated estimate of about one minute per trip on average. It is not a measured value, and not all blood takes the same route. Flow speeds are typically described as 20 to 40 cm/s in the aorta, 0.3 to 1 mm/s in capillaries and 10 to 20 cm/s in the vena cava, but sources and conditions (resting or peak, average or maximum) give a range. William Harvey argued in his 1628 book, by estimating how much blood the heart pushes out, that blood does not keep being made but circulates. He was not the sole discoverer: the flow through the lungs had been described earlier by people such as Ibn al-Nafis (13th century) and Servetus (16th century), and Harvey did not predict capillaries. This piece leaves out heart valves, blood pressure, blood components and exercise. All numbers are rough guides, and nothing here is for diagnosis or health advice.