High availability is an integrated feature of RHEV and allows for virtual machines to be restarted in case of a host failure.
HA has to be enabled on a virtual machine level. You can specify levels of priority for the vm (e.g. if resources are restrained only high priority vm are being restarted). Hosts that run highly available vm have to be configured for power management (to ensure accurate fencing in case of host failure).

Fencing Details: When a host becomes non-responsive it potentially retains the lock on the virtual disk images for virtual machines it is running. Attempting to start a virtual machine on a second host could cause data corruption. Fencing allows RHEV-M to safely release the lock (using a fence agent that communicates with the power management card of the host) to confirm that a problem host has truly been rebooted.

RHEV-M gives a non-responsive host a grace period of 30 seconds before any action is taken in order to allow the host to recover from any temporary errors.
Note: The RHEV-M manager needs to be running for HA to function (unlike e.g. VMware HA or Hyper-V HA that do not rely on vCenter / VMM for the failover capability), also HA can not be enabled on the cluster level.