The album received an average score of 82/100 from 13 reviews on Metacritic, indicating "universal acclaim".

[3] AllMusic writer Thom Jurek praised the album for being a maturation of Pallbearer's sound, saying that it manages to not forsake the band's origins while still breaking new ground.

[5] Writing for Exclaim!, Trystan MacDonald said, "Heartless continues to build on the band's reputation as one of the biggest acts in doom metal.

"[8] In a more lukewarm review, Pitchfork contributor Andy O'Connor wrote, "The deep cauldron of metal, prog, and doom influences have so far been a key to Pallbearer's greatness, but their third record fails to piece it all together.

"[12] PopMatters writer Tanner Smith was very positive on Heartless, calling it a sign that Pallbearer will go down as one of the best metal acts of the decade.