Game version: Latest as of posting; unsure
Operating system: Windows 10
Tiles or curses: Tiles
Mods active: None that affect healing items
The interface shows the amount of health that will be gained over time.
The interface shows zero health gain.

Get hurt and use a healing item.
This UI window was not changed and will show instantaneous healing from items (as it was before).
It is not possible to precisely calculate net healing from effects, because it will depend on taking damage, sleeping, mutations and other factors. You can see healing power of the item (intensity of applyed effects) in the item description.
We either need to display something useful in this menu or trim it down to just listing the body parts.
Most helpful comment
We either need to display something useful in this menu or trim it down to just listing the body parts.