The effect of the Heart Container in both games is simple, it will reduce 100% of damage of the player who picks it up. Any damage taken during the healing will be subtracted from the final amount. In SSF, All-Star presents three Heart Containers on the All-Star Rest Area that player may use between rounds, unlike in Super Smash Bros. Melee, these Heart Containers do not reduce damage all the way down to 0%, only the habitual 100%. It used to be the best recovering item until the introduction of the Energy Tank in SSF2, which is able to reduces the damage of the player to 0% but at the expense of vulnerability, which may hinder its healing factor and may recover less than the Heart Container.
The Heart Container made its first appearance in The Legend of Zelda. At the beginning of The Legend of Zelda, Link starts off with three hearts. When Link can either buy a Heart Container from a merchanter or get one by beating a boss. Once he gets the Heart Container, it gives him one heart unit to his life meter; however, it does not used to replenish any of his health. In The Legend of Zelda: Link's Awakening, when Link finds a Heart Container, it gives him another heart and replenishes all of his health. This was also true in The Legend of Zelda: Ocarina of Time and The Legend of Zelda: Twilight Princess. In Super Smash Bros., the Heart Container reduces a character's damage to 0%, but in Super Smash Bros. Melee and Super Smash Bros. Brawl, it only recovers 100% max. Nevertheless, the recovery is not instantaneous in any game and a player can still take damage whilst recovering. In Super Smash Bros. and Melee, the Heart Container appears as it does in The Legend of Zelda: Ocarina of Time. Its appearance changed in Brawl to its The Legend of Zelda: Twilight Princess appearance, similar to Link, Zelda, and Ganondorf. Being based on Melee, SSF uses Ocarina of Time's design; but SSF2, instead of Twilight Princess' design as Brawl did, uses the design from The Legend of Zelda: Skyward Sword. It, however, used to have the design of Twilight Princess, being redesigned thrice, before being changed to Skyward Sword's design.
Super Smash Flash
Heart Container, as it appeared in Super Smash Flash.