The Hearts atop each Customer order represents that Customer’s patience. After you serve the Customer their order, their remaining Hearts will fill up the Heart Meter. Once the Heart Meter is completely full, your current Customers will get their Hearts refilled.
What is a Heart Gem?
When a Customer with full Hearts is served, they may drop a Heart Gem. Use the Heart Gem to fill up the Heart Meter completely and restore everyone’s Hearts to 3!