To the atheist, there is nothing more damaging to the pursuit of truth than involving one's heart: it is with a clear head, not an emotional heart, that we can realise how specious theistic arguments are (e.g., a miraculous healing becomes a lot less miraculous when you see it for what it is).
MY BROTHER,
It is primarily in the secular West that the heart has become wrongfully defined as the seat of a person's emotions--Valentine's Day, fat little kids with bows and arrows, soap operas and Harlequin Romance novels, etc. In spiritual considerations, this definition is 180 degrees from reality and REAL Love, of course, is not an emotion but a decision (which, of course, explains why over half of all marriages end in divorce.)
i am really loath to go into this subject because, like most spiritual matters, it is hard to comprehend and even harder to communicate accurately--especially for me (i am rather slow in these areas.) May i just quickly hit the high points--the basics--as i see them. Others, i'm sure, would differ, and i would be loath to defend my particular ideas given that i have heard many different explanations of these matters and all appear plausible to me. So . . .
Scripture teaches that human beings were created as triune beings, with a physical body, a mind, and a spirit. Our bodies are, in a sense, the seat of our material existence and allow us to physically function in the material universe which God has graciously provided for our existence and pleasure.
Our minds, as i see it, are basically infinitely intricate computers designed to process and utilize data provided by our bodies and our spirits and to direct our lives by allowing informed choices to be made based upon the outcome of the data processed.
Our spirits, on the other hand, are the "spark of God" within us which allows us to communicate with God and to understand that communication and respond to it appropriately. It is the "breath" God breathed into man at the time of his creation.
Then there is the heart. (Again, i must stress
as i see it, as others more qualified than i would probably explain it differently [although i think perhaps the differences are more semantic than functional, words being the slippery objects they are]). The heart, to my understanding, is the seat and center of our being. Its function is primarily to make decisions based on the data provided by the mind and the spirit, and then live out those decisions. Thus, you might say that the heart is the center of our being--our identify which, because we are created in "the image and likeness of God," is primarily spiritual rather than material.
The above is highly inadequate and grossly superficial, i know, but it is the best i can do with my limited understanding and capabilities.
And how does one connect the heart and mind?
Because of mankind's rebellion against God--"original sin", if you will--our direct communication with God though our spirits was broken and we died spiritually as God promised--"You shall surely die." When this break in direct access to God occured--i look at it as having the cable system unplugged

--Scripture says that our hearts turned to stone and ceased to function as they were created to. In this vacume, the mind of man took over control and, being informed only by material data from the body and the physical environment, turned us in on ourselves and our ego-centric little universe and left us fumbling in the dark, caught in an existence that was more dead than alive--with the disasterous results we see today. (It is very easy to see why atheists consider human beings as animals because of what we have become!)
To re-unite the mind with the heart, the residence within us of God's spirit must first be reestablished--a process described by God as "replacing your hearts of stone with hearts of flesh"--which was the primary reason for God's incarnation and His life, death, and resurrection.
Once the spirit has again taken up fully functioning residence within, the mind will be forced to reliquish control and the system--as created--will be returned to it proper balance, with the spirit in primary control and the person thus under God's control. It is only then that the mind can return to the heart and, in proper balance, process data from both material and spiritual sources and act as the directive choice-making source of man's existence by forming a synthesis of spiritual and physical inputs and judging rightly the correct life-course for the individual to pursue based upon God's will and material
realities (as opposed to illusions.)
What does the heart do that the mind cannot?
The mind, as mentioned above, when functioning in isolation, gives a very lopsided picture of reality due to a lack of sufficient data--"garbage in, garbage out" in computer terms. It must be informed by spiritual realities to be able to function in a healthy and effective manner. The idea of the "mind in the heart" is that the heart--the center of a person's being--is the crucible where God is able to blend, according to His will, material and the spiritual realities into a continuous unique path for each of His children to follow in order for them to live lives of maximum happines, peace, and joy through living lives of service to others to the glory of God.
i apologize for the muddledness above! If i were to go back through it and try to organize it better i would probably delete the whole thing so i'll just leave it be and hope it answers at least one of your questions.
ephraim