Use your supply of Hearts to challenge friends, or accept challenges that were sent to you!
You'll be able to see how many Hearts you have available for challenges at the top right corner of your screen when you're on the challenges tab.
Hearts replenish automatically at a rate of one Heart every 4 hours, up to a maximum of 3 hearts.
Out of Hearts, but want to play more? You can purchase refills instead of waiting, by tapping on the green "+" button on your Heart meter.