Heart Pots () allow you to carry one extra Heart. Naturally, the more Pots you have, the more hits you can potentially take before you reach game over.
You start the game with five Heart Pots, and therefore, lives, and you can find or buy more, up to a maximum of nine, throughout the game. They can be bought most commonly from Swap Meet Pete in his store for 250 crystals, and after collecting nine, he will say "I'm sorry Croc. You are only allowed to have nine! It's the law!"
Note that when you die and continue, you will only receive three Hearts out of a maximum of nine to play with, no matter how many Heart Pots you're carrying. All of your Heart Pots will be filled when you purchase a new one, or when you collect all 100 crystals from a particular stage.