Hundred of years ago in England, many children dressed up as adults on Valentine's Day. They went singing from home to home. One verse they sang was:
Good morning to you valentine;
Curl your locks as I do mine---
Two before and three behind.
Good morning to you valentine.
In Wales wooden love spoons were carved and given as gifts on February 14th. Hearts, keys and keyholes were favorite decorations on the spoons. The decoration meant, "You unlock my heart!"
In the Middle Ages, young men and women drew names from a bowl to see who their valentines would be. They would wear these names on their sleeves for one week. To wear your heart on your sleeve now means that it is easy for other people to know how you are feeling.