Contradiction with Proverbs 28:26
This verse emphasizes trusting one's own heart, in contrast to Proverbs 4:23's warning to guard the heart above all else.
Proverbs 28:26: He that trusteth in his own heart is a fool: but whoso walketh wisely, he shall be delivered.
Contradiction with Jeremiah 17:9
This verse describes the heart as deceitful, contradicting Proverbs 4:23 by suggesting that guarding it may not be beneficial.
Jeremiah 17:9: The heart [is] deceitful above all [things], and desperately wicked: who can know it?
Contradiction with Matthew 15:19
This verse states that evil thoughts come from the heart, contradicting the idea that the heart is something wholly positive in Proverbs 4:23.
Matthew 15:19: For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies:
Contradiction with Mark 7:21-23
This passage lists negative things originating from the heart, opposing Proverbs 4:23's implication of the heart as a pure wellspring of life.
Mark 7:21-23: Thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride, foolishness: [covetousness...: Gr. covetousnesses, wickednesses]
Contradiction with Ecclesiastes 9:3
This verse notes the prevalence of evil in the hearts of men, suggesting a contrast to the ideal protection of the heart in Proverbs 4:23.
Ecclesiastes 9:3: This [is] an evil among all [things] that are done under the sun, that [there is] one event unto all: yea, also the heart of the sons of men is full of evil, and madness [is] in their heart while they live, and after that [they go] to the dead.