Assalaamu 'alaykum ukhti
You ask a good question, one I've often wondered myself, and May Allaah subhanhu wa ta'ala reward and increase you in good for this concern. How many walk around with blackened hearts and not a care in the world? This conscience is definitely a sign of goodness, and I pray this increases.
I looked up the hadeeth for it, and I believe it has your answer:
The Prophet (peace and blessings of Allaah be upon him) said: “If the believer commits a sin, a black spot appears on his heart. If he repents, gives it up and seeks forgiveness, his heart is cleansed, but if he does more then (that spot) increases until it covers his heart. That is the raan (covering of sin) which Allaah mentioned in the Qur’aan:
“Nay! But on their hearts is the Raan (covering of sins and evil deeds) which they used to earn”
[al-Mutaffifeen 83:14]
Narrated by al-Tirmidhi, 3334; Ibn Maajah, 4244; classed as hasan by al-Albaani in Saheeh al-Tirmidhi.
You see? The conditions are to repent, give it up and seek forgiveness from Allaah and Allaah is most wise, and most Forgiving so if you're sincere and trying to change your ways it's definitely in the way of trying to cure this problem which exists in all of us, and is a constant struggle subhanAllaah.
May Allaah makes it easy on All of us!
BaarakAllaahu feeki
wasalaam