Because we did work at constant pressure, and so it's just volume difference times pressure.

因为是在恒压下做功，所以功就等于体积变化乘以压力。

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As it does that it changes the volume of the heart and gives the - creates the pressure that moves blood around your body, so it has that muscular system.

这使心脏的体积发生变化,产生了足以使血液流遍全身的压力,这就是心脏中有肌肉系统的原因

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