You can get more than the 3 Hearts you start off with in Forager by using Spirit Orbs to increase it, but what is the max Health you can have in Forager before you reach the cap? The answer is that you can have a total of 18 Health / Hearts in total, and at that point you won't be able to increase it any further.
Since you start off with 3 Hearts, you will need to use 15 Spirit Orbs to get your Health to maximum if you only focus on upgrading your Health.
When you have all 18 Hearts, you will have all three rows filled. Each hit from an enemy will deplete 1 Heart / Health, so at this point it's going to be difficult to die.
Anyway, that's all you need to know about the max health you can have in Forager, so good luck getting all the Spirit Orbs needed to reach the cap of 18 Hearts.