I have heard that Silphium (the worlds first contraceptive) was the basis for the heart symbol. Its seed was shaped like our heart symbol, and its connection to sex, lust, and love were the reason it was chosen to depict these things for centuries. Down below is a link to an image of a coin that depicts the Silphium seed:
http://images.mylot.com/userImages/images/postphotos/1543883.jpg
Hi Yairh20, and welcome to the SDMB.
It’s customary to include a link to the article in question, for threads like these - I think this is the one that you’re referring to:
The Perfect Master has also held forth on the subject of Silphium as contraceptive in ancient Rome. No mention of the shape of the seeds, however.