How To Get Golden Hearts In Terraria

HEART CRYSTALS

You must gather Heart Crystals from Underground areas, the Underworld, or the Dungeon, all of which are easier to explore before unlocking Hard Mode. These are Large Red heart-shaped crystals that give off a slight red glow/sparkle. You must "break" them with a pickaxe (edit thanks to RianBattle). Once you obtain a Heart Crystal, you put it in your top row and "use" it with . Your character will hold it above their head and a green 20 will appear, which increases your max health by 20 (or one heart), accompanied by a chimey sound. You have maxed our your health from heart crystals when you have two full rows of hearts, and when holding one up no longer produces a green 20 (it takes 15 heart crystals in total).
NOTE: This is different from the hearts that creatures drop, which restore 20 lost health points.

MANA CRYSTALS

For mana, you must collect stars that fall from the sky at night. You can increase their drop rate with a Star Fury sword, or by wearing a Star Veil. You must then craft these into mana crystals (fallen stars are yellow, and mana crystals are blue), which can be done anywhere without a crafting station needed. It takes 5 stars to make one mana crystal. You use these the same way as heart crystals. Each one increases your max mana by 20, and it takes 9 mana crystals to completely max out your mana total, since you start with one. Mana naturally refills itself over time.
NOTE: This is different from the blue stars that creatures drop, which restore 200 lost mana points.

LIFE FRUIT

You also need 20 Life Fruit as well to get complete maximum health. These are found in a Jungle after Hard Mode is unlocked and you kill one mechanical boss.(credit to Calex dEUS) They come from cutting down the foliage in a Jungle Biome. They look like a Gold Heart surrounded by a green heart outline. You use these the same way as heart crystals. Each of these increase your max health by 5 and will turn one of your red heart into a gold one, increasing your max health by a total of 100 (which takes 20 Life Fruit) for a grand total of 500 health. Your health is completely maxed out when you have two full rows of gold hearts.

TIPS/TRICKS

1. This is another achievement easily completed via the duplicating method for the three items. Or you can get them from a friend who has saved them after getting max health/mana.
2. Your max health/mana is saved to your character, so you can use multiple worlds to farm the items, including other players' worlds.
3. These items are only found, they are never sold by NPCs or dropped from creatures.

***Same as 360 version***

NOTE: xMidgetFuryx said:

Just want to note if you import a character from your Xbox 360 that is already maxed out you will not unlock the achievement.

You could use that character to import the necessary items into a world and leave them for a new character, but you definitely need to max out a character to full health to get the achievement.