"Keep thy heart with all diligence; for out of it are the issues of life" Proverbs 4:23
Some of the things we have to be on guard for that want to take our hearts prisoner and hold them hostage are bitterness, unforgiveness, self-pity, anger, resentment, condemnation, false religion, guilt, jealousy, hate, envy, malice, etc. (plus many more I haven't named).
If these aren't dealt with, they will hold your heart in a prison as long as you allow them to. They will not only hold it prisoner but turn it into something that it wasn't intended to be and unrecognizable-- stone.
There is only one sure way to keep your heart. Give up claim to it. Turn it over to the Lord and let Him take full possession of it. Does this mean that these things won't come again to try to reclaim it? No, but it is much easier to keep from giving in when you realize it doesn't belong to you anymore. So, when these things come to take your heart prisoner again, simply put out a sign that says, "This heart does not belong to me anymore. You will have to go to the owner-- Jesus".
Have a great day. There are so many things that want to destroy, possess and imprison our hearts. But when we give up ownership of our hearts to Jesus, they can't.