I always use this macro on all my healers
Code:
#showtooltip
/cast [@mouseover,help,exists] [@target,help,nodead] [@targettarget,help,nodead] [@player] Soothing Mist
Change Soothing Mist to any one of your healing spells, so you just need to over your mouse on any of your party members and use the macro. What this does is cast, in this case, Soothing Mist on my mouseover whatever it may be; if I'm not mouseovering any player, it casts the spell on the player I'm targeting; if there's no one as my target, it casts on myself.
See if this one works on your case