Charles Ellicott Commentary Jeremiah 4:9

"And it shall come to pass at that day, saith Jehovah, that the heart of the king shall perish, and the heart of the princes; and the priests shall be astonished, and the prophets shall wonder." — Jeremiah 4:9 (ASV)

The heart of the king shall perish. —The heart, as representing the mind generally. Judgment and wisdom were to give way to panic and fear.