Heroes of the Storm - Free Hero Rotation Week of Tuesday, July 28, 2015

Week of Tuesday, July 28, 2015:

Malfurion
Valla
Tyrael
Zagara
Chen
Tyrande (Available after you reach player level 12)
Illidan (Available after you reach player level 15)

Source: http://eu.battle.net/heroes/en/forum/topic/13604571130?page=2#26