Thanks a lot for the feedback!! Yeah, right now even with the max amount of cells working on the heart it's only possible to heal up when there's zero injuries. I noticed too that when there are more and more injuries the health goes down way too fast.
I never really thought I would be that much difficult, that goes to show how important it is to have someone else playtest, rather than doing it yourself, knowing exactly how everything in your own game works.
I'll play with the numbers a bit and try to make everything more balanced. Thanks!