There is a lot confusion on how SCOM heartbeats work so I am going to try to explain. First In SCOM there are really only two important pieces or entities.
This first is the Windows Server entity which encompasses everything about a server except heartbeat.
The windows server entity looks like this
The heartbeat or agent watcher entity looks like this.
Now when you create a subscription to this group you will get alerts for everything related to the server and the hearbeats.