What are lives(hearts) and how to refill them?

You start the game with five lives. 

Whenever you fail a level, you lose one life. 

Lives are automatically replenished over time – one every 30 minutes.

You can cut the wait and refill lives with coins, or request a heart from your team

In addition, you can gain "Unlimited lives" for a certain amount of time by purchasing it from the shop or by getting it as a reward from many of the fun features