There are several synonyms for the phrase "be out of breath." One common synonym is "pant," which refers to the heavy, rapid breathing that often occurs after physical exertion. Another synonym is "gasp," which often suggests a sudden, desperate need for air. "Wheeze" is another synonym, often used to describe breathing that is labored and accompanied by a whistling or rattling sound. Other synonyms for "be out of breath" include "puff," "pant," "respire," "puff and blow," and "heave." These synonyms can be used to add variety and nuance to descriptions of physical exertion or moments of intense emotion.