Here's another word citation I somehow missed on the same site:

>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.<

I know we've covered the phrase "wearing your heart on your sleeve" on this board before...anybody recall if this was the origin we came up with?