Here "heart" refers to the whole person, and "turning away" means to stop obeying. Alternate translation: "who no longer obeys Yahweh our God" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
Moses speaks of someone who secretly worships another God as if he were a root, and the evil deeds he does to serve that god, and which he encourages others to do, as a bitter plant that poisons people. Alternate translation: "any person who worships idols and causes others to disobey Yahweh" (See: [[rc://en/ta/man/translate/figs-metaphor]])