There is a phrase in Bereshit/Genesis 6:5 which reads in hebrew: '.... v'kol yetzer machshevot libo...'
I found different translations starting of with: The entire, every, the whole.. And ending with: imaginations of/from the heart, thoughts or ideas from/of the heart, every plan divised, inclination/impulse etc.
It seems that it's not the heart which is evil, but the Yetzer machshevot which comes from the heart. So what exactly does the wording 'Yetzer machshevot' mean and learn?
And what does it mean that it was evil from the early period (youth) of the human being (Bereshit 8:21)?