system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how does my heart beat 100,000 times a day for 80 years without getting tired or messing up?

it just amazes me. i thought the heart was a muscle. it never stops.
gpt
The heart is a muscle, but it's a different type of muscle from your skeletal muscle. Cardiac muscle cells have 10 times as many mitochondria as your skeletal muscles. Mitochondria are basically the "power plants" of your cells that break down glucose into energy. Because they have so many mitchondria, they have a basically endless supply of energy. Also, the heart beats rhythmically, with different parts contracting and relaxing at different times, so when one part is contracting, the other part is not doing anything, meaning every part of your heart gets a "micro-rest" during each heartbeat.