The first valentines were sent in the 15th century. But not until the 17th century did people start exchanging cards and letters. And Valentine's Day cards weren't mass-produced until the 1840s.
Wearing your heart on your sleeve is more than just a phrase. In the Middle Ages, young men and women drew names to see who their Valentine would be, the LA Times reports. According to Smithsonian, they would wear the name pinned to their sleeve for one week so that everyone would know their supposed true feelings.
Did you know that pet owners buying Valentine's gifts for their beloved animal is big business? Nearly 10 million pet owners buy Valentine's gifts for their pets each year