I think imagining yourself kissing their hearts is a fine devotion you have made for yourself. It is an act of love and that love will reach Jesus and Mary; don’t know that the actual kisses will touch their hearts in heaven. However, the love that motivates it will.
Will God take back your heart and sanctify it? Absolutely. But we have to do our part as well. Sometimes we just have to downright refuse to sin using our will. In my experience, when I have used my will to stop a particular sin, I’ve noticed an infusion of grace. I remember when I gave up pornography years ago. I just had to absolutely refuse to do it and get into something else that day. Finally the day ended without me using it. Then I did the same thing the next day–kept busy, said my prayers, asking God to give me the grace to stop and then that day came to an end without my doing it. After a few days, I noticed a mysterious change. I didn’t want it as much as I did before. But it took time to stop. And on and on it went until I finally stopped. God changed my desires.
I’ve read several saints and visionaries who’ve said basically the same thing–God wants us to fight sin ourselves using our strength of will. I think sometimes we as Catholics are praying but we forget that we have to do our part in the battle. He will give us the grace but we have to fight first. Once God sees you are fighting, the grace will flow and he will change your desires and begin to sanctify you. And if you are fighting and you are still falling just keep it up. Don’t give up, no matter what! That’s what the devil wants.
“Even if you are committing mortal sins, keep on praying and I guarantee that you will reach the harbor of salvation.” St. Teresa of Avila
God Bless!