Health Refills are power-ups that can be found in the game. As the name suggests, they refill Mickey's health. They resemble a pink version of Mickey's head with a white heart in the main "head." They come from defeated enemies or from breakable/painted objects. At first they refill one health pip, but later in the game they refill three as well as one. After a while they start to shrink (though this doesn't affect their refilling properties) and eventually disappear completely.
In Epic Mickey 2: The Power of Two, the item retains it's use, though sometimes can disappear immediately and without warning. The reason for this is unknown, though it is possible that it is a glitch.