'Heart' in the Bible

For our witness does not come from error or from an unclean heart or from deceit:

But we, my brothers, being away from you for a short time, in body but not in heart, had all the more desire to see your face;

And last of all, the prayer which we make to you from our heart and in the name of the Lord Jesus, is this: that as we made clear to you what sort of behaviour is pleasing to God, as in fact you are doing now, so you will go on in these ways, but more and more.