1) A defensive implement, of wood or metal, sometimes circular, sometimes heart-shaped, secured to an arm by loops or a strap.
2) Her. The stylised heart shape used as the field for an "escutcheon. By the time of Edward, the Black Prince (d. 1376), the arms shown on a shield would depend on the occasion of use. There were shields for arms of war and shields of peace, with different arms for use at a "tournament. In Edward's case, the arms of war were the arms of England, whereas his arms of peace showed three ostrich feathers "argent on a field of *sable. -
Cf. Pas d'armes
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.