Most Christians believe that their heart is an opponent; a cancer to be beat, or an unruly dog to be tamed.
Usually, they've ended up with that belief because, though their beliefs came from the bible, they weren't biblical. The belief that their heart is still corrupt and wicked even after Jesus has taken up residence there, was often formed, not from a composite and whole picture from Scripture, but from select passages ripped from context.
Until about 8 years ago, I too had developed what I thought was a biblical assumption about my heart and its motives: concluding that my heart would lead me astray because it was attracted to sin.
Here are some of those select passages and even worship songs upon which many Christ-followers have built a theology that assumes their heart is still wicked:
"Create in me a pure heart, O God, and renew a steadfast spirit in me." [Ps. 51:19]
[You might remember the Keith Green song here.]
"The heart is deceitful above all things and beyond cure." [Jeremiah 17:9]
"Prone to wander, Lord I feel it. Bind my wandering heart to thee." [Hymm: "Come Thou Fount']
Cherry-picking selected passages and forming a complete theology would be like eating each ingredient of a cake by itself: First, eating the raw eggs, then eating the half-cup of salt, then eating the raw flour. The whole and completed cake tastes nothing like the individual ingredients separated-out.
Your heart is your ally now: aligned with God's own spirit. Your heart is your advocate, not your adversary.
Here's a modern translation of what Luther affirmed over 300 years ago:
"For faith in Christ gives us the Holy Spirit, who gives us new hearts, and stirs those hearts so that we may now willingly pursue God's best." -Martin Luther
Your heart is your ally, not your enemy.