The phrase "heaving sigh of relief" is often used to describe the feeling of being relieved after a stressful or anxious situation. However, there are a number of other synonyms for this phrase that can be used to equally express the same feeling. One such synonym is "breath of relief", which suggests the release of tension through a deep exhale. Another option is "exhale of relief", which emphasizes the act of exhaling as a way of letting go of stress. "Sigh of contentment" can also be used when the feeling of relief is accompanied by a sense of satisfaction or happiness. Ultimately, the choice of which synonym to use will depend on the context and tone of the situation.