There are 3 health upgrades in the game, each granting you an additional heart.
They can all be bought from a character in Iripur (character to the left of the blacksmith).
Upgrade 1: 1 Ore, 130 Gold
Upgrade 2: 1 Ore, 290 Gold
Upgrade 3: 1 Ore, 400 Gold
Check out this awesome guide for Ore locations:https://steamcommunity.com/sharedfiles/filedetails/?id=81020...