The number of lives (hearts) indicate the number of attempts you have to complete a level. You start the game with the maximum number of five lives.

Each time you fail to complete a level, you lose one life. One life is replenished every 30 minutes, so you can quickly return to having 5 lives 🙂

You can find the number of lives you have by checking the heart icon at the top of the home page. If you don't want to wait 30 minutes, you can also click on the heart-shaped icon on the right side of the home page.