Although the heart symbol can be traced back many generations, nobody is really sure how it took on its current meaning. A leading theory contends that during the seventh century B.C., the silphium plant was used as a form of birth control in the city-state of Cyrene. Legend has it that the plant was so important to the local economy that “coins were minted that depicted the plant’s seedpod, which looks like the heart shape we know today,” according to Slate.