The phrase "change heart" implies a change in someone's desires, beliefs or feelings. Antonyms for this phrase could include "remain steadfast," "stay committed," "maintain resolve," or "stay true to oneself." Alternatively, "flip-flop," "waver," or "oscillate" could be used to describe someone who changes their opinion or mind frequently. Another antonym for "change heart" could be "stay unmoved" suggesting someone who is unswayed by opposing perspectives or arguments. Whatever the antonym, it is clear that the phrase "change heart" denotes a shift or alteration in one's disposition, making the opposite connotation quite straightforward.