Synonyms of heartlessly

2 Syllables
coldly, meanly
3 Syllables
brutally, fiercely, unkindly, ruthlessly, viciously, brutishly, callously, ferally
4 Syllables
hardheartedly, unfeelingly, coldheartedly, murderously, ferociously, relentlessly, savagely, mercilessly, atrociously, barbarously, inhumanly, pitilessly
5 Syllables
unrelentingly, inexorably, barbarically, demoniacally, diabolically, inhumanely, remorselessly