Cupid's Arrows were fired by Cupid. If a mortal was struck by one, they would fall in love with the next person or creature they saw. If the target of the spell was already in love or had met their soulmate, then the memory of that person could potentially break the spell. Hercules was once shot accidentally and fell in love with Psyche. He was able to break the spell by thinking of his true love, Deianeira (HTLJ "The Green-Eyed Monster").
Bliss stole the arrows in "A Comedy of Eros" and wreaked havoc between Xena, Gabrielle, Joxer and Draco.