The phrase "crosses one's heart" is an expression that refers to making a promise or vow about something. The antonyms of this phrase would be statements that express doubt, uncertainty, or dishonesty. Words such as "lie," "gossip," or "betray" can be used as antonyms for the phrase. When one doesn't "cross their heart" about something, they are not making a commitment and are thus being dishonest or untrustworthy. In contrast, when we do "cross our hearts", we are being truthful and sincere with ourselves and others. Hence, antonyms for this phrase essentially denote falsehood, disloyalty, or deception.
