Also, on someone's heels . Immediately behind, in close pursuit. This idiom is used both literally, as in Jean's dog was always at her heels , and figuratively, as in Although his company dominated the technology, he always felt that his competitors were on his heels . This idiom appeared in the 14th-century romance Sir Gawain and the Green Knight . The expression is sometimes intensified as hard on someone's heels or hot on someone's heels . Also see on the heels of