Romans 2:14-16

For when Gentiles, who do not have the law, by nature do what the law requires, they are a law to themselves, even though they do not have the law. They show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them on that day when, according to my gospel, God judges the secrets of men by Christ Jesus.

Matthew 15:19

For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander.

Jeremiah 17:9

The heart is deceitful above all things, and desperately sick; who can understand it?