system
Given the following post, respond as if you're commenting on Reddit:
human
Why doesn't our heart get tired even after beating for our entire lifetime?

It essentially is a muscle, and exercising it continuously should get it tired, right?
gpt
The heart is made of a different type of muscle cell: Cardiac muscle.

Unlike smooth and rough muscle (that makes up every other muscle in your body), cardiac muscle evolved to be tireless.

They have a lot more mitochondria than normal muscle, allowing them to produce more ATP. This prevents muscle fatigue.