Well, if you turn your head 180 degrees, it kinda looks like a heart. That's why people use it. Kidding. Nobody's quite sure, but it might have to do with a North African plant. During the seventh century B.C., the city-state of Cyrene had a lucrative trade in a rare, now-extinct plant: silphium. Although it was mostly used for seasoning, silphium was reputed to have an off-label use as a form of birth control. The silphium was so important to Cyrene's economy that coins were minted that depicted the plant's seedpod, which looks like the heart shape we know today. The theory goes that the heart shape first became associated with sex, and eventually, with love.