Valentine's Event 2016
The Valentine's 2016 Event is an event that start 6/Feb/2016 and lasted until 14/Feb/2016. During this time users were to obtain 
Sweet Hearts and send out Valentine's Cards to other users.
If you were able to send a card to three (3) different users, you would be able to obtain a brand new Event Pokemon on February 14th.
Valentine's Cards
Every Valentine's Card cost 50 Sweet Hearts each to send. You have the option of attaching a message or anonymously sending the Card, though neither of the two are required.
Sweet Hearts
Sweet Hearts are obtained by interacting or by sending a Dream World Plushie to another user.
Once obtained, they could only be used to send Valentine's Cards to other users. Sweet Hearts are not recycled to the following year's Valentine's Event.