Heart Containers are items found in The Legend of Zelda series. They are heart-shaped crystals that increase Link's maximum HP by one heart. Full Heart Containers are typically dropped by bosses and Link can also create one by combining four or five pieces of heart. They've appeared in nearly every game in the series excluding Zelda II: The Adventure of Link for the NES.
Heart Containers also appear in the Super Smash Bros. series, where they will reduce the damage percentage the player has by 100% in All Star Mode and completely in regular battles.