In the favorite novel of my youth "Anne of Windy Willows" (aka "Anne of Windy Poplars", but I somehow prefer the Willows version for the vivid visual image the title invokes), Anne Shirley gives a piece of her philosophy of mind.
"My brain agrees with every word you say but my heart simply won't," said Anne. "I feel, in spite of everything, that Katherine Brooke is only a shy, unhappy girl under her disagreeable rind. I can never make any headway with her in Summerside, but if I can get her to Green Gables I believe it will thaw her out."
(From L.M. Montgomery's Anne of Windy Willows).
In the context of referring to the emotional and sentimental dispositions with which one goes about in one's life, "heart" equals "brain". It is at least so from the modern brain scientific point of view. However, the wisdom of folk psychology often distinguishes the two, as the above Anne Shirley quote tells us.
The phenomenology of the conscious mind, as it is based entirely on the activities of neurons, is in essence bound to the brain. It is interesting to see how the word "heart" is used as a means of extending one's sensitivities beyond this limitation. Anne is trying to make the life brighter for her deprived colleague Katherine Brooke, and is thus trying to go beyond the borders of individualities. The colloquial expression "heart" as opposed to "brain" thus might reflect our often unconscious wish to go beyond the dichotomy between the Dionysian and the Apollonian sensu Nietzsche.