Unicast mode with single adapter

Hello,

There are conflicting info about the heartbeat communication in Unicast single mode.

"Heartbeat messages are transmitted over NLB Enabled NIC always whether you're operating cluster in Unicast or Multicast mode"

source : http://support.microsoft.com/kb/556067

In other places it says host to host communication cannot take place in Unicast single adapter mode.

1) Is the host to host communication same as the heartbeat messages which are send by every host every second?

If it cannot takes place, then how is the cluster converging and thus cluster working?

OR is it that host to host communication is something other than heartbeat ?

Any help is appreciated.

Thanks