How to do damage?

Heys,
I would like to add spell damage for enemies to my heal macro(s)? In other words heal if a help target and damage if a harm target.

Here’s an example of what I have so far…

#showtooltip
/cast [mod:shift,@player] [@mouseover,help,nodead] [help] [@targettarget,help,nodead] Flash Heal

How do? THX

The body pulling Priest. (And tired of it)