Heartbeat Down Counter

How do I make a simple counter, that show how many of my hosts are down?

We are running heartbeat.
I'd think it was simple to make this, but I can't figure it out.

How do I make a simple counter that show how many of the lastest pings to hosts have returned "down"?

Or can I make a treemap or Donut or something, so I can also know which hosts those are.

This is probably really obvious, but I can't figure out how to make this. Seems like a common use-case.

EDIT: I just checked the server that is down, via Discover, and Heartbeat just stops checking the server when it dies? Then what is the point of Heartbeat? How do I then check if my servers are up or down? I thought that was the whole idea behind Heartbeat? Have I misunderstood something?