# Energy consumption/Power output of human heart

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The average heart pumps 4.5L of blood along 100,000km of blood vessels once per minute.
Shouldn’t this take ungodly amounts of energy? (KE = 1.74×10^9 Joules)
But that’s much higher than the calories a human consumes in a day, let alone a minute, let alone just by the heart muscle.
Can anyone explain to me how the heart is able to push all that blood all that distance?

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How have you calculated that number? I am genuinely curious

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KE is kinetic energy and if we assume a blood density of 1 kg/l the speed ov the blood need to be 27808m/s for that energy. I had assumed you calculate the kinetic energy by assuming 4.5l of blood travel 100,000km each minute but 27808 * 60 =1.6 million meters or 1600km.

But any calculation like that is flawed for any reason, one is that all blood does not travel the total distance of all blood vessels. If you pour water between two balls with two instead of one identical pipe the travel distance has not double, you do not have two pipes of the same lenght with having the water flow in each. The water flow distance is the same.

When a drop of blood will make a single loop in your body and should be somewhere around your double your body length for the longest path. Blood vessels do not go the shortest path but they to do not go around in circles. So the speed of around 4meter/minute is a more reasonable speed if all blood is pumped around once per minute

Even if that was the speed of the water you can use kinetic energy to calculate the power you need to sustain that speed. That number is the energy required to reach that speed, to keep it you only need to overcome forces that slow you down.

Compare in a car the power and fuel usage during acceleration compared to constant high speed where you only need to overcome air resistance

The power of a human heart is around 1 watt according to https://hypertextbook.com/facts/2003/IradaMuslumova.shtml

You can calculate it by multiplying the flow rate with the pressure the heart adds. For an adult the heart pump around 6 liters per minute = 10^-4 cubic meter per second. The pressure of the heart is around 10^4 pascal and 10^-4 * 10^4 = 1 watt

I’m not up to speed on your exact calculation, but a big flaw I suspect is that the 4.5L does not travel the complete 100,000km. It will split up so that only fractions are travelling any kind of distance.

This is also without fact checking your 4.5l.or 100,000km figures.

not a physics person so i cant really judge about the energy part and can only provide little input

but you have to consider that there are other things that an complicate the thing

for example the heart is elastic and not a physical metallic pump and the elasticity of the heart muscle and the vessel does help to maintain the blood pressure along with many other hormones to help it do what it does

there is even skeletal muscles that help push things from down to up and the 100 000 km vessels arent all going to be the same size that might change things even more