I was thinking about the phrase "I love you with all of my heart" and I was curious as to its origin.
Here are some past answers:
http://www.reddit.com/r/AskHistorians/comments/1fitq1/when_where_and_why_did_the_heart_become_the/
While there's no total answer to your question, they do discuss elements of it. The biggest component is that the cultural connection isn't universal.