What is another word for in a heartless manner?
Pronunciation: [ɪn ɐ hˈɑːtləs mˈanə] (IPA) 
There are many synonyms for the phrase "in a heartless manner," which refers to acting or behaving without any compassion or kindness. Some alternative phrases that convey a similar meaning include "cruelly," "mercilessly," "callously," "coldly," "indifferently," "ruthlessly," "unsympathetically," "unfeelingly," and "inhumanely." These words all imply a lack of empathy or concern for others, and they suggest a certain degree of harshness or brutality in one's actions or attitudes. Using these synonyms can help to add variety and emphasis to your writing, and can convey a different tone and mood depending on the context.
