I got mine on the first wizard I encountered. I cleared the bar room area, camped out, checked some stuff on the bazaar, came back found him, killed him, looted heart.
I was a 52 wizard at the time of the killing
Inferno Goblins are second to Solusek goblins in difficulty. They are found throughout Solusek's Eye, and are typically encountered around the bar area of the Castle.
The wizards can be paritularily dangerous, and despite their low HPs, can cause significant amounts of damage in a short time.
Like all casters in Solusek's Eye, the Wizards can see invisible.