How does the Heightened rule work with Wholeness of Body?

I still don’t understand the Heightened rule.

I have a level 4 monk. If he gets "Wholeness of body" which heals for 8 pts and has: Heightened (+1) If you choose to regain Hit Points, the Hit Points regained increase by 8

How much Hps does he get at level 4 and at level 5 ?