The antonyms for the phrase "changing heart" are fairly straightforward. The idea of a changing heart implies that one is open to new ideas or experiences, and is willing to alter their beliefs or attitudes based on new information. The opposite of this would be a "closed heart," where one is unwilling to consider new perspectives, or a "unchanging heart," where one's beliefs and attitudes are firmly set and cannot be swayed. Other possible antonyms might include "hardened heart," "fixed heart," or "rigid heart," all of which describe someone who is resistant to change or growth. Ultimately, the opposite of a "changing heart" is anyone who is stuck in their ways and unwilling to embrace new ideas or experiences.