Source : Webster's Revised Unabridged Dictionary (1913)

Heartrending \Heart"rend`ing\, a.
   Causing intense grief; overpowering with anguish; very
   distressing.

Source : WordNet®

heartrending
     adj : causing or marked by grief or anguish; "a grievous loss"; "a
           grievous cry"; "her sigh was heartbreaking"; "the
           heartrending words of Rabin's granddaughter" [syn: {grievous},
            {heartbreaking}]