Re: Heart in martial art ?
I'm guessing that a lot of the heart's "special" nature could be explained by understanding the autonomic nervous system, and (I'm guessing) possibly the nature of cardiac muscle. Yes, the autonomic nervous system is neural tissue, and yes, cardiac muscle is muscle tissue, but they also have unique characteristics. You can't somehow train the rest of your body, the rest of your nerves and muscles, to take on these characteristics.
As for the metaphorical use of the term "heart", that seems to be to be referring to characteristics of the human consciousness - which, call me Betty Buzzkill if you want, but I can't imagine residing anywhere but in the brain.