When preparing your Virtual Infrastructure environment for vSphere 5 and vCenter 5 you also need to think of all the vCenter applications that are dependent on vCenter. One of them is vCenter Heartbeat. To be able to run vCenter Heartbeat on vCenter 5 you will need to upgrade vCenter Heartbeat to version 6.4. Normally upgrading vCenter Heartbeat isn’t a big deal but there has been a change from 6.3 Update 1 to 6.4. Where you could normally use a configuration of “identical nodes”, you will now have to switch to “non-identical nodes” according to KB 1014435.
From the KB article: “Important: When performing an upgrade to vCenter Server Heartbeat 6.4 from 6.3 Update 1 with Identical nodes or from any previous version, you must first migrate from Identical nodes to Non-Identical nodes before performing the upgrade.”