Well, everyone knew about the heart and basic organs, because animals were eaten in those days. There was no great surgery but still there was some medical science.
So, heart being the primary part of the body, even historically and logically we know people knew about heart and mind(at-least their importance, if not how to FIX them).
And if we take this in general, that if prophet knew about each part of body in detail? than I think we can't say, but it is highly unlikely. His role and duty was being a messenger of Allah. Not being a surgeon or a scientist. If Allah would had told him the details of human body and organs, he would have surely told them to us.
"I am only a human being. When I command you with something regarding
your religion, accept it. When I command you with something from my
own opinion, know that I am only a human being. You know worldly
affairs better than me." (Muslim, Fadail, 140-141)
So, we don't say what we don't know. Or what has not reached us.
Allah knows best