Special Hearts are a relatively rare item from Yoshi's Story. They are required to open up new levels in subsequent pages, which act as the game's worlds. Each page in the game has four levels; however, only the first level of the subsequent page can be accessed unless a Special Heart is collected in the current level. This applies to all pages past the first, where all four levels on the first page can be accessed at the beginning of the game. Instead of playing through each level in a page, the player only gets to play through one level on a page before moving on to the next page.
In each level, there are three Special Hearts hidden throughout the stage. Ringing chimes will sound when a Baby Yoshi is close to a Special Heart. Each Special Heart opens up a new level on the next page, which means that all three Special Hearts are needed to unlock all the levels on the next page. Basically, more Special Hearts means more options for levels in the next world. As such, Special Hearts must be collected in order to have access to every level in the game.