There are a plethora of synonyms for the word "cold-heartedly". Some of these include unkindly, callously, mercilessly, pitilessly, ruthlessly, unsympathetically, heartlessly, unfeelingly, and insensitive. Each of these words carries a slightly different connotation, but all describe a lack of compassion or empathy for others. Depending on the context, certain synonyms may be more appropriate than others. A writer may choose to use one of these alternatives to add depth and nuance to their writing, or to avoid repetitive language. Regardless of which synonym is chosen, they all convey a sense of emotional distance and indifference towards others.