A heartbeat is a signal (like a ping) that one component sends to another at a regular interval, so that the other component knows that the sender of the signal is still out there.
If the entity listening for the heartbeat does not hear it within a set amount of time, it knows that the sender of the signal might be in trouble.
In the RFID system, the Data Capture and Delivery controller has a heartbeat to the reader to make sure that the reader is still there. The controller also heartbeats back to the WebSphere® Premises Server. If WebSphere Premises Server does not hear the heartbeat from the Data Capture and Delivery controller within the timeout period, it assumes that the controller is down or disconnected.
The heartbeat from the Data Capture and Delivery controller to the WebSphere Premises Server contains the current status of the heartbeats from the controller to the tag reader. The WebSphere Premises Server can tell from the Data Capture and Delivery controller heartbeat if the tag readers are down.