itch.io

Thanks, there are already medkits that spawn with a 1/40 chance for every zombie killed that give you one additional heart.

There is a dropping sound when they spawn and an exclamation mark on the mini map.

I think that was the reason why I decided to use hearts instead of a health bar, so you can see it  more clearly if one is gained or lost.
Of course something different than the standard heart would have been more original.