This is probably one of the tougher things to write about, because there are no easy answers to a hard heart. In some circumstances you may be able to recognize it in yourself, and if you are unfortunate enough to experience hardness of heart when it comes from another there may be very little that you can do about it.
Scripture has lots to say about the heart, not least of which comes these words:
“The heart is deceitful above all things, and desperately sick; who can understand it” (Jeremiah 17:9).
There are warning signs that a heart is hardening; judgment, callousness, rudeness, disregard, frustration, and more. Whenever you get to the point of wanting to dismiss another, you are getting one step closer to a hard heart.
Hard heart’s are notoriously hard to break. Once an injury and impression is firmly settled it is hard to dislodge, the other has been firmly established. Even if a peacemaker comes along to try and reconcile a hard hearted person to another they will be met with the fiercest and most irrational of resistance.
Hard heartedness is a prerequisite for all wars, all lawsuits, and all disintegrating families. A lack of compassion is the catalyst for countless sorrows, and worst yet the diminishing possibility that any wrongs will ever be made right.
There’s a reason that Pharaoh’s heart is made hard. For hardness of heart can not be overcome by willing the mind to do the right thing. Hard hearts work especially well among the proud and well educated, because hard hearts are the last thing people of youth, means, and status expects to find in themselves.
A hard heart is a deceitful thing often leaving the person to whom it afflicts unable and unwilling to change.
So who can rescue us from the misery of the miserly heart? Only Jesus himself. Only the Spirit of God can help us repent and change. May the Spirit of God be able to convict you today if you are going down the road of the callous heart.
Can you think of a circumstance where you may have come across a hard heart in a relationship? Are you able to recognize your own hard heart habits? Invite Jesus to convict you of any hard heartedness today.
May you always retain a heart of compassion,
Alexei
The Missional Life 
Jealousy, envy, pride and bitterness (unforgiveness) all can and do cause a hardened heart. The only remedy is total surrender to our loving and trustworthy Abba Father, but it’s a very difficult thing for our worldly flesh to let go of those troublesome things.