As nouns the difference between heartlessness and heatlessness
is that heartlessness
is the characteristic of being heartless while heatlessness
is the state or condition of being heatless; absence of heat.
Heartlessness is a derived term of heartless.
As a noun heartlessness
is the characteristic of being heartless.
As a adjective heartless is
without a heart; specifically, without feeling, emotion, or concern for others; uncaring.