The Collaborative International Dictionary of English v.0.48:

Heartless \Heart"less\, a.
   1. Without a heart.
      [1913 Webster]

            You have left me heartless; mine is in your bosom.
                                                  --J. Webster.
      [1913 Webster]

   2. Destitute of courage; spiritless; despondent.
      [1913 Webster]

            Heartless they fought, and quitted soon their
            ground.                               --Dryden.
      [1913 Webster]

            Heartless and melancholy.             --W. Irwing.
      [1913 Webster]

   3. Destitute of feeling or affection; unsympathetic; cruel.
      "The heartless parasites." --Byron. -- Heart"less*ly,
      adv. -- Heart"less*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

heartlessness
    n 1: an absence of concern for the welfare of others [syn:
         heartlessness, coldheartedness, hardheartedness]