text: A long time ago, before people knew what the heart was really used for, it came to be associated with strong emotion.  Whenever you feel strong emotion, there's a sensation on the left side of the chest.  We now know that sensation is actually caused by chemicals in the brain.  Back then, people didn't know that.  They just assumed that the heart controlled emotion.  Even know we know better now, the old associations still stick with us, as they have become so ingrained in our culture.