Jeremiah 17:9 in the World English Bible
The heart is deceitful above all things and it is exceedingly corrupt. Who can know it?
Context
8 For he shall be as a tree planted by the waters, and that spreadeth out her roots by the river, and shall not see when heat cometh, but her leaf shall be green; and shall not be careful in the year of drought, neither shall cease from yielding fruit.
9 The heart is deceitful above all things, and desperately wicked: who can know it?
10 I the LORD search the heart, I try the reins, even to give every man according to his ways, and according to the fruit of his doings.