system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly happens to your heart when you have to inject it with an adrenaline shot?

The needle always seems huge and one would think that stabbing yourself in the heart would cause some damage.
gpt
The needle is very long so that it reaches the heart.  It's pretty far in there.  It's not too big around, and your heart is a big muscle, so it can close the hole without too much trouble.  The adrenaline is a strong stimulant, which gets the heart pumping harder and faster.