I can add detail to the first part of your question, but not the second. Nor do I think the two parts are necessarily related.

There are anatomical, symbolic, and spiritual reasons why emotions have been associated with the heart in Western traditions. Greek (Galenic) medicine posited that a fundamental element of life was heat and the source of the body's vital heat was the heart. The heart's placement next to the cooling lungs allowed for the alleviation of its occasional passionate or emotional excitation. These anatomical assumptions were compounded by the heart's place in the passage of blood through the body:

The ancient art of phlebotomy or bloodletting ... was essentially a method by which residues that have accumulated in the blood because of too much nourishment could be removed in order to restabilize the equilibrium of the humoral body. The doctrine of pure and impure blood was a physiological analogue to the Judeo-Christian notion of the ambivalent heart housing a variety of good and evil impulses, pure and impure thoughts and intentions (R.A. Erickson, The Language of the Heart: 1600-1750, 1997).

The sigificance of the heart as the site of emotional, spiritual, and symbolic functions varies between Judeo-Christan traditions. It was very strong among, for example, early modern nonconformists. Here is a typical Scruptural analysis written by the seventeenth-century puritan, John Owen:

The heart in Scripture is taken for the whole rational soul ... as all the faculties of the Soul are one common principle of all our moral operations. Hence it has such properties assigned unto it as are peculiar to the mind or understanding, as to see, perceive, to be wise, and to understand; and on the contrary, to be blind and foolish; sometimes such as belong properly to the will and affections, as to obey, to love, to fear, to trust in God (J. Owen, Pneumatologia, 1676).

So as the site of the 'whole rational soul', the heart is the channel through which the will and the affections (among other things) are passed. This kind of language -- which easily lends itself to the idea that the holy spirit will, or will not, penetrate the heart of the unregenerate for spiritual correction -- can also be found in other prominent protestant theologians, including Luther and Bunyan.