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Comment by fluoridation

12 hours ago

Cardiac tissue is also a volume. It can be thicker or thinner as the animal requires.

Yes, but the force of a muscle does not increase with volume, but only with its section.

So a bigger heart would need to have thicker walls in comparison with its internal volume, which would increase disproportionately the volume of the heart walls, so for bigger and bigger hearts the useful internal volume that is filled with blood would be a smaller and smaller fraction of the total heart volume.

The lower efficiency of a bigger heart would require a higher contraction frequency to compensate, but the bigger a heart is the smaller is its maximum contraction frequency, due to the small speed of the propagation of an excitation through muscle cells and nervous cells.