I found this post from Richard from another thread:
Richard Launius wrote:
1) Some hero cards seem to be perpetual and they are POWERFUL cards, are any Hero cards perpetual?
No. There are no base level Hero cards that are perpetual, all are discarded when used. There are 2 exceptions on the higher level power (power that the player pays gold to use) that are ongoing for more than 1 turn as noted below:
Dwarf: Golden Touch - for an investment of 3 Gold the Dwarf gains 1 extra Gold from Supply each time they take gold from the supply or another player.
Wizard: Mystic Shield - for an investment of 3 Gold, the wizard blocks all wounds from the dragon 3 times. Then the shield spell fizzles out.
Full thread here:
Hero Cards Targeting Other Players