Is the hardened heart literal or figurative? Would you feel anything with a hardened heart like as if you're about to cough because you're heart feels some physical thing? Or is it figurative and you can't feel anything at all? or some arrogant person?
On the authority of Abu 'Abdullah al-Nu'man bin Bashir (ra) who said: I heard the Messenger of Allah(sas) say:
"The halal is clear and the haram is clear, and between them are matters unclear that are unknown to most people. Whoever is wary of these unclear matters has absolved his religion and honor. And whoever indulges in them has indulged in the haram. It is like a shepherd who herds his sheep too close to preserved sanctuary, and they will eventually graze in it. Every king has a sanctuary, and the sanctuary of Allah is what He has made haram. There lies within the body a piece of flesh. If it is sound, the whole body is sound; and if it is corrupted, the whole body is corrupted. Verily this piece is the heart." [Bukhari & Muslim]