The heartbeat is a key LifeKeeper for Windows fault detection mechanism. The heartbeat is a periodic signal sent over the comm path between a pair of servers. The regular signals tell each server that the other is still active. When you define your comm path, the definition sets the heartbeat signal interval in seconds and specifies the number of consecutive heartbeats a server can miss before marking the comm path as dead.
When the LifeKeeper for Windows servers mark a comm path as dead, inter-node communications immediately commence over the comm path with the next highest priority. Only when the server fails to receive the heartbeat signal on all comm paths does LifeKeeper for Windows initiate the safety check to determine the need for failover recovery.