heart of the matter

What is the origin of the iconic representation of the heart (such as on a playing card)?

I don’t think that anyone knows for sure.

My own pet theory based on the medieval heart shape before it evolved into the fatter modern version, is that it was originally based on the shape of female genitalia.

I’ve always thought that it was based on the shape of leaves that prisoners used to scratch out messages on. I have no idea why I believe this.

From Heart symbol - Wikipedia]Wikipedia

Real hearts are have two lobes, are tapered at the bottom, and are rounded at the top. (Take a look at images of pig or cow hearts, for example – something that people would have been much more familiar with than human hearts.) The “heart” shape is an iconic representation of this. I don’t see why you need to go looking for an alternate explanation.

Cecil’s brief response to the question: How come valentine hearts don’t look anything like real hearts? - The Straight Dope