I use:

#showtooltip
/cast [target=focustargettarget,help,nodead,exists] Healing Wave; [target=target,help,nodead,exists] Healing Wave; [target=player] Healing Wave

on my shamans, it heals the member being beat on by the focustargets target. Also if you're targetting a party member, everyone heals that member, and if nobody is targetted then they heal themselves. I have yet to have any problems with this macro.