The Collaborative International Dictionary of English v.0.48:

Heartbreak \Heart"break`\ (-br[=a]k`), n.
   Crushing sorrow or grief; a yielding to such grief. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

heartbreak
    n 1: intense sorrow caused by loss of a loved one (especially by
         death) [syn: grief, heartache, heartbreak,
         brokenheartedness]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "heartbreak":
   aching heart, affliction, agonizingness, agony, anguish, bale,
   bleeding heart, broken heart, brokenheartedness, care,
   desolateness, desolation, dole, excruciatingness, excruciation,
   grief, heartache, heartbrokenness, heartsickness, heartsoreness,
   regret, rue, torment, tormentingness, torture, torturousness,
   woe