The passage, "Create in me a clean heart, O God, And renew a right spirit within me" (Psalm 50:12 - Orthodox Study Bible) would be applicable to one who has undergone a heart transplant. Organ transplantation has been accepted by most Orthodox.
My point wasn't about organ transplant itself, I'm more interested in the ideas that underlying ideas that some Orthodox hold to. For example:
"The heart is the center, the mid-point of man's existence. And not only in the spiritual sense, where heart is the term for the center of one's spiritual person, one's "I"; in physical life, too, the physical heart is the chief organ and central point of the organism, being mysteriously and indissolubly connected with the experiences of one's soul.
It is well known to all how a man's purely psychical and nervous experiences joy, anger, fright, etc.,—are reflected immediately in the action of the heart, and conversely how an unhealthy condition of the heart acts oppressively on the psyche and consciousness... Yes, here the bond is indissoluble—and if, instead of the continuation of a man's personal spiritual-bodily life, concentrated in his own heart, there is imposed on him a strange heart and some kind of strange life, until then totally unknown to him—then what is this if not a counterfeit of his departing life; what is this if not the annihilation of his spiritual-bodily life, his individuality, his personal "I"
? And how and as whom will such a man present himself at the general resurrection?"
I was trying to show that some Orthodox would seem to agree with the original idea that the heart was considered to be very important to a person, part of what made him, part of his essence, etc.