Welcome to the club of people who stare at the screen for 3 seconds every time they toy with heartbeat package/service and initially get a problem until they remember...
Funny story actually:
I don't use deb packages, but use "heartbeat-elastic" for the service name. That's the right name everywhere, except where it isn't like the binary itself.
This is a useful read to hopefully burn it into your brain enough so that it only takes 3 seconds of starring when you hit this again in six months. I promise, it's a only a very small annoyance once in a while in exchange for a very cool name
I believe this page is simply wrong, I guess even the people at Elastic get confused sometimes? Or they use variables to build part of the doc:
Do you want to open an issue for what I think is bad doc above and reference this thread? Let me know if you can.