hi, dear sacred star,
i have jus finished writing a research about the importance of heart in Islam. you know what? the prophet Muhamamed says that there is an organ in man's body if it is good then all his things are good, but ib this organ is bad then all hi/her things are going to be bad. this organ is the heart.now the experts in the field of human devlopment argues whatever you think you may get it. Alghazali( one of the sufis) tried to explain the importance of heart and he comes to announce the following: when you think negatively the evil comes to your heart asking you of doing more bad things, but if you thik positively the angel responds, coming to your heart, inspiring you of more good things. accordingly, there is a deep relation between the way of thinking and the result of your doings. god says : whoever believe in God, will God guide his heart. so, if you thik of something yuo nwill get it.
I also agree with brother I-Brian, for there is a deep link between heart and reasoning and mind, for God says: eyes are not get blind, but the hearts which are in the breasts.
with my best wishes