The heart is deceitful above all things and beyond cure. Who can understand it? (NIV)

The heart is deceitful above all things, and it is exceedingly perverse and corrupt and severely, mortally sick! Who can know it [perceive, understand, be acquainted with his own heart and mind]? [Matt. 13:15-17; Mark 7:21-23; Eph. 4:20-24.] (AMP)

The heart is deceitful above all things, and desperately wicked: who can know it? (KJV)