system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What starts the pumping of the human heart and how does it keep going?

I guess I’m asking how the heart works, like what’s the power source?  I keep thinking of an engine which needs a method to turn on and to keep going.  I sound dumb.
gpt
You don't sound dumb. It's a good question. The heart has its own electrical system that keeps it pumping independent of brain function. Sometimes it misfires, though, and that can lead to things like heart attacks. Basically, as long as there's blood flowing through the heart to keep it alive it doesn't even need to be in the body. That's what they do for heart transplants.