I'm curious. How high can I get?
I believe 400 health is max, 20 health per heart and start with 100 health, so 15 crystal hearts.
EDIT: This is current as of v1.0.4
EDIT2: It should be noted that max mana is 200, or 10 mana crystals.
Using Life Crystals, you can get up to 20 hearts or 400 max health.
After you have 400 health and defeat Wall of Flesh to enter Hardmode, you can consume up to 20 Life Fruit to get to 500 max health. Life Fruit are found in the Underground Jungle and give +5 to max health.
You will need 15 Life Crystals and 20 Life Fruit to get to the maximum of 500 health.
The maximum health you can get is 600 in total.
You will need to use 20 Life Crystals to get to 400. To get to 500, you will need to defeat Wall of Flesh to get in Hardmode, smash a Demon/Crimson Altar and defeat a Mechanical Boss so Life Fruits can start growing in the Underground Jungle. You must firstly get to 400 health to be able to use a Life Fruit.
Lastly, you can get to 600 health for 5 minutes by using a Lifeforce Potion which increases total health by 20% and are sometimes found in Shadow/Lihzahrd Chests or crafted with:
a Bottled Water
a Prismite(a fish)
and 5. a Waterleaf
The Lifeforce Potion is crafted at a Placed Bottle or a Alchemy Table.