It's in the Bible

I read this in Matthew last night:

18But the things that come out of the mouth come from the heart, and these make a man 'unclean.' 19For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, slander.

That's from Matthew 15.18-19. And I was thinking about how we treat our hearts. That sounds somewhat odd. But I wonder if evil thoughts and some of that other nonsense that is coming out of our mouths, if it's because of a lack of concern on our part for the condition of our heart. I think of people who don't guard their hearts, like co-workers. And then I hear the way they talk and I see their actions. And I know it's a heart issue.

So how do you treat your heart?