The Heartbeat Server is a central component of the Presence architecture.
It allows for centralized control over the main Presence services, including:
The Heartbeat Server runs as a Windows service on one physical or virtual machine. In a typical installation this will be the same machine as the Database Server, although there is no reason why it can reside elsewhere.
The Heartbeat Server is responsible for launching the Presence Server and Database Server if they reside on the same machine, and so it is important to ensure that the Heartbeat Server has the permissions required to access any files or resources that the Presence Server will need to access. For this reason it is often a good idea to create a Windows account that the service can run as.