How does the heart deceive itself? It's because the heart is fallen. Satan doesn't need to be there and considering Satan isn't omnipresent that he may require his demons to tell them what Christians are doing, he doesn't even need to be there. Satan is a dangerous and cunning adversary but he doesn't even need to be there to make the person sin. While he did lead Adam and Eve to sin to eat of the forbidden fruit but one cannot deny that Satan may have not been there when Cain killed Abel. God warned Cain of sin crouching at his door. Maybe Satan arranged Cain to kill Abel as some Christian cartoonists may suggest. The problem has been the sinfulness of the human heart so blaming Satan for you falling into sin doesn't count. It's because man has that sin problem in their hearts and Satan can't be there all at once to influence everyone to sin. Demonic doctrines and media are more than enough to influence the sinful heart to lead people into sin.
Thinking of the many crannies where vanity hides, the many holes where falsehood lurks, it's so decked out in hypocrisy that it leads to self-deceit. Isaiah 44:20, Jeremiah 49:16, Romans 16:18 and James 1:26 addresses how the heart is self-deceived. How many bad decisions were made because of the sinfulness of one's human heart! How much self-vanity leads to pride, where so many lies are inside the heart that leads to habitual lying, to how much hypocrisy is in the heart of every man all because of the sinful condition of the heart!
The remedy is in Ezekiel 11:19 and 26:26 declares the LORD's provision for a new heart. Rejoice oh repentant sinner for the LORD Himself offers a new heart. He says that He's come to give a new heart to take away that stony heart and replace it with a tender heart that will love God. That is the heart of the new nature which helps the Christian overcome the stony heart. There's much hope that by the grace of God the human heart will learn to love the LORD. That is His declaration of deliverance from a heart that loves sin to a heart that loves the LORD.