Hearts are used to play stages in Stage Mode. Each stage requires one heart to play.
The heart counter replenishes every 30 minutes, up to a maximum of 5. Hearts obtained from other sources, such as reward boxes or from the gift box, can make the counter go over this limit. In any case, reaching 5 or over will reset the timer, so it's a good idea to wait for the timer to reset, replenishing one heart, before claiming any heart rewards.
Hearts can also be replenished by spending Diamonds, using the popup that appears when clicking the plus icon next to the Heart counter at the top. The rates are:
- x5 -> x10
- 60 minutes of infinite play! -> x30