I started to look around for some more articles to see what has been said about whether the Fathers, when speaking of the heart, really referred to the physical heart or to a non-physical, spiritual heart. I haven't really found much online, but I did find something else on orthodoxinfo from Fr. John Romanides (http://www.orthodoxinfo.com/phronema/pa ... -nous.aspx). In footnote number 3, he seems to interpret St. Gregory Palamas's referral to the heart as not meaning the physical heart, but rather to the "deep heart". So it seems that there may be some disagreement on this matter.
What is rather interesting is that when I was searching for more Orthodox references about the heart, I found some secular studies that have arisen about the function of the heart, arguing that it functions more than just as a pump.
Some other food for thought (I have not found any writings on this, this is just my own thoughts on the topic) is that it does seem that God deemed that the physical heart be tied to our souls, because whether the heart is still beating or not determines whether we still have time to repent. Virtually all of our other organs could fail, but as long as our heart is still alive, we still have time to repent and save our souls. But once our heart stops, there is no more time left.
Father Anastasios, have you found any other writings on whether the Fathers were referring specifically to the physical heart? I have found plenty of references to the heart in the writings of the Fathers, but not much in the way of whether they meant the physical heart or not.
(PS. I was loaned the tapes that I mentioned in the previous post; hopefully I will be seeing the people who loaned me the tapes soon so that I can find out the name of the tapes).