Heart shards can be found in their ore from underground.
When you eat a heart container it gives you another permanent heart.
When you hold the heart container (recipe below) you will get 1 more heart. Your hearts will stay after you die. To get 3 rows of hearts, you need 135 heart shards. The ores spawn underground near the iron level and are pretty common, they can also be found in structures or from mob drops.



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