The human heart is mentioned almost 300 times throughout the Bible.
Of course we are not talking about the organ that pumps blood but the inner part of a person. Our heart is our core, spiritual self which is then expressed through our minds. We know that God has a heart too since we read that David was "a man after God's own heart."
Jeremiah 17:9 states that "the heart is deceitful above all things and desperately wicked: who can know it?" We don't have to look far to see that the natural tendencies of people are deceitful and twisted. Our heart produces thoughts and feelings which are filtered through our minds and then turned into actions. Everything we do begins in our heart.
As believers, we don't have to live a live of failure, settling for a "deceitful heart" as our lot in life. We actually have control over the condition of our hearts. If we have God's word in our hearts, our lives will be guided and fulfilling. Our relationship with God draws our heart closer to Gods heart making us look more like God the more time we spend with him.
We should find comfort, knowing that since we were made in God's image and God is our teacher, that He is our best cheerleader too! He is not keeping an eye on our hearts just waiting for us to make mistakes and correct us. 1 Thessalonians 2:4 says "God examines our hearts [expecting our best]."
When God looks at our heart, His eyes are full of grace and love and positive expectation.
God knows us far better than we even know ourselves (Romans 8:27) and desires more than anything for a deep relationship with us. This is how David got the title of "man after God's own heart".
Our prayer should be as Davids: "Search me, O God and know my heart: try me and know my thoughts..." and that we will guard our hearts above all else, for it determines the course of our lives. (Proverbs 4:23 NLT)