How to implement heartbeat diagnostic in ros2 system

I would like to check whether each node on my system is alive or not, and I found there is a class Heartbeat that seems to be doing this. I am not so familiarised with classes and, thus have no idea where to start with.

Say under the ros2 workspace, there are two nodes, minimal publisher node and minimal subscribe node. How can I implement this heartbeat diagnostic into this system? Also, how does it know which node name to find for?

Any guidance is appreciated.