Looking for potion trigger help

I cant seem to figure out how to make a trigger that works when you use a potion (Item) which heals the unit using it over time. So click potion > heal unit for 50% oh total hp over 5 seconds. but it want this to be independent of the item so they can use it over and over if they want to and it stacks.

Thanks
Bustaboom

The trick is to use a "local" variable with the same name as a global variable. This ought to work:

Create the global variable "ItemHealTarget" (unit).

You are awesome thank for very much