heartlessness vs hardheartedness

heartlessness and hardheartedness both are nouns.

Word	Noun	Adjective	Verb	Adverb
heartlessness	Yes	No	No	No
hardheartedness	Yes	No	No	No

As nouns, heartlessness and hardheartedness are synonyms defined as:

heartlessness and hardheartedness: an absence of concern for the welfare of others

Other synonyms of heartlessness include coldheartedness.

heartlessness (noun)	hardheartedness (noun)
an absence of concern for the welfare of others	an absence of concern for the welfare of others