Wearing Your Heart on Your Sleeve is a phrase used to describe someone who is prepared to show their affection openly and obviously. During the Middle Ages, and the great tournaments where noble knights battled for honour and prestige, it was common for a lady to 'give her heart' to a knight at such occasions in the form of a handkerchief or other token of affection.

The knight would then enter the lists with the lady's 'heart' pinned to his sleeve, for all the spectators to see.