system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do our hearts beat 24/7 without needing to take a break/rest period?
gpt
They’re hyper-specialist cells for just this purpose.  Cardiac muscle cells ditch all the storage space and reproductive parts and max out on mitochondria.

100% power all the time.

They don’t need to save fuel, they’re in the heart and have first dibs on fuel.

They don’t need to have regenerative capacity, you’re double dead if you take damage there anyway and they’re encased in a bone shield

They don’t need to worry about waste buildup - just dump it into the passing blood flow.

They don’t need to manage temperature changes, they’re deep in your core and well insulated.

All the things normal muscle cells have to worry about don’t matter, just max power all day every day.