Personification of the Heart

How did the heart become the organ for love?  Because of my lack of important things to wonder about and utter worry free world, I am fascinated by the way this organ is personified in literature, music, and film.  The heart is often referred to as "broken" or "crushed", people can "rip it out and stomp on it."  Things are described as being done "half hearted", sometimes the heart "cries out" for something.

Heart necklaces are often given as gifts, but would they lose their charm 

if instead of receiving this:

You received this? 

Or, how would you feel if you received the organ more accurately accountable for our feelings?

The Brain on a Chain