The VMware - Virtual Machine Heartbeat alarm shows the status of communication between the VMware VirtualCenter and the VMware Tools on the virtual machine.
When an Information alarm is raised
VMware Tools are not installed or are not running.
When a Low severity alarm is raised
There is an intermittent heartbeat. This may be due to guest load.
When a Medium severity alarm is raised
There is no heartbeat. The guest operating system may have stopped responding.