The phrase "over in a heartbeat" refers to a situation or event that ends quickly, almost instantly. Antonyms for this phrase could include "never-ending," "long-drawn-out," "protracted," and "extended." These words describe situations that are ongoing or continuing, and can be used to express a sense of time dragging on endlessly. Additionally, "over in a heartbeat" implies a spontaneous or unexpected ending, so antonyms might also include phrases like "predictable," "routine," or "ordinary" which suggest a more natural or expected conclusion. Overall, the antonyms for "over in a heartbeat" convey a sense of time that is slow or predictable, in contrast with the sudden, fleeting nature of the original phrase.