Appreciation Hearts

This currency is characterized by its icon representing a single red heart.

As soon as this currency is unlocked to you, your Heart Wallet will be found at the top of your screen at any given moment.

There exist several methods for you to obtain Appreciation Hearts:

Click on thought bubbles from happy Peeps and there's a chance a Heart or two will drop. It's your Peeps' way of rewarding your good management with their love!
Place Security Guard buildings in your Main Park. Each copy will produce Hearts for you to collect after some time.
Place Life Guard buildings in your Water Park. Each copy will produce Hearts for you to collect after some time.
Visit your Friends' Parks daily. There's a chance you'll be able to collect some Hearts during your visit!
Watch Advertisements to trigger a Fireworks Show.
Spin the Casino Wheel. There's a chance for the reward you will obtain to be Hearts.
Head to the Store and purchase a Heart Pack or Bundle that includes Hearts!

There are several ways for you to spend your Appreciation Hearts:

Send a Peeps Train to boost your revenue.
Collect your Main Park's Coin earnings at once in the Park Office Landmark.
Trade your extra Cards for higher rarity Cards in the Trading Fair Landmark.
Send an helicopter to obtain a specific Card in the Heliport Landmark.
Obtain certain Cards in the Mall Landmark.
Spin the Casino Wheel once everyday. (Note that after the first time, Tickets will be exchanged instead.)

You can start collecting Appreciation Hearts from your happy Peeps as early as Level 10, but will only be able to use them once you reach Level 20.

Your Heart Wallet is shared between all your Parks.