Heart Fruit

As the Yoshis in Yoshi's Story look for the Super Happy Tree, they follow a trail of fruits. One of these fruits is the Heart Fruit. The Heart Fruit makes Yoshi invincible and stronger and sometimes reveals some extra coins in the level within the time limit. The fruit can also give the Yoshi some health. The Heart Fruit looks like a red heart with a face on it. Some are big, some are small. If a Yoshi eats a Black Shy Guy while being invincible, the Yoshi gets hurt and the invincibility magic cuts off as the Yoshi is back to normal.

Purpose
The Heart Fruit is the fuel for the Super Happy Tree. Without it, the tree wouldn't be a happy tree and the Yoshis on the island wouldn't be happy.