MAX UP Heart

HP-Up Hearts (known as HP Plus in Europe) are special hearts Mario can find during his adventure in Paper Mario: Sticker Star. As the name implies, these hearts will increase Mario's maximum HP by 5 and will fully refill his health bar. It also increases the attack power of his First Strike by one for every two collected. There are 16 HP-UP Hearts to find and by collecting them all, Mario will have a total amount of 100 HP.

Paper Mario: Color Splash
In Paper Mario: Color Splash there are six of them and each time Mario and Huey collects a Big Paint Star, their maximum HP will increase by 25. If all six are collected, then he'll have a grand total of 200 HP.

Trivia

 * HP-Up Hearts function in a similar way as Heart Containers from The Legend of Zelda series, by increasing the player's maximum health and refilling it completely when obtained.