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]