Source : Webster's Revised Unabridged Dictionary (1913)

Heartburning \Heart"burn`ing\, a.
   Causing discontent.

Heartburning \Heart"burn`ing\, n.
   1. (Med.) Same as {Heartburn}.

   2. Discontent; secret enmity. --Swift.

            The transaction did not fail to leave heartburnings.
                                                  --Palfrey.

Source : WordNet®

heartburning
     n : intense resentment; "his promotion caused much heartburning
         among his rivals"