The heart shape was around long before it was associated with the human heart. It can actually be found in artwork dating all the way back to the 13th century. Playing cards have had the image of the heart since the 15th century.
For many years people have speculated about what inspired the heart’s shape. The most common theory is that it represents part of the female anatomy. Some theorize that it’s the buttocks as viewed when bending over. Some think it’s the shape of the breasts, the pubic mound, or even the spread vulva. Others think it’s the male testicles, the head of cupid’s arrow, or the shape of two swans.
As cool as the theory of two human hearts fused together is, sadly this can’t possibly be true. Humans didn’t know what a real human heart looked like till Leonardo Da Vinci drew one in 1511 and the drawing wasn’t actually published till 1519. Even then it wasn’t circulated widely with the public because the findings for the drawing came from examining a fetus, and many though Da Vinci was ignoring God’s teachings.
Personally, I like the idea of two human hearts fused together. I know it looks a little gross, but it's kinda romantic too. What girl doesn't like a little romance?