try monitoring your Zenoss system with the Unix top utility. The heartbeat is basically saying that the central zenhub daemon has not received a heartbeat from colector daemon(s). This does happen occasionally if the box is busy.
Is it the same daemon(s) that keeps giving heartbeat errors or do you get a kluge where they all report heartbeat errors? If the former, it may be a problem with that daemon or its workload (like zentrap getting flooded with TRAPs for example). If the latter scenario then it is more likely to be a Zenoss server performance issue.
Cheers,
Jane
