Mario does not gain extra health if he is already affected by a Life Mushroom. Upon grabbing a second one, his health will restore to 6. If Mario grabs a Life-Up Heart while he has 6 health points, it will give him coins instead.
The player can find the Life-Up Heart before boss battles, or in challenging levels. It is also sold in the Crazy Cap stores, will sell Mario a Life-Up Heart for fifty regular Coins, and won from slot minigames. One can be found inside a ? Block in the Metro Kingdom, before the Mecha Wiggler's boss fight. A bonus Life-Up Heart can be obtained once a day by scanning the Wedding Princess Peach amiibo. A Life-up Heart can also be obtained in the Darker Side either by defeating the Yoofoe at the start of the caverns or correctly answering the sphinx's question: which kingdom has he not been to yet (the answer is the Mushroom Kingdom).