The phrase "with all one heart" implies complete dedication and sincerity towards a particular endeavor or goal. Antonyms for this term would connote a lack of commitment, half-heartedness, or a general disinterest. Antonyms for "with all one heart" could include phrases such as "with insincerity" or "with half-heartedness." Other possible antonyms could be "apathetically," "indifferently," or "unenthusiastically." These terms suggest a lack of passion, motivation, or sincerity towards the task at hand. It is important to be committed and passionate when undertaking anything in life, as this is often the key to achieving success and fulfillment.