A colleague in Kalimdor, Apothecary Helbrim, is researching the effects of Lordaeron toxins on the beasts of Kalimdor. He would be very interested in a sample of the wolf hearts Renferrel sent me.
Helbrim is stationed in the Barrens, in a village known as the Crossroads. To reach him, you must travel via zeppelin to the orc capital of Orgrimmar, then travel south, by foot, to Durotar. Head west into the Barrens, and you will soon reach the Crossroads.