The Heart of Caizehl is the city-font of Mhaldor, bestowed upon them by Sartan in the year 807AF.
After the destruction of the Fissure, Mhaldor sought a way to restore their font. Within the depths of the tunnels that Moghedu dug in order to assault the city with aid from the Tsol'teth, a great pit was dug and subsequently filled by Mhaldorians as they sacrificed their life essence and blood in service to Sartan. Once it was sufficiently filled, they sacrificed an Avatar of Evil, Taryius Lichlord, in order to consecrate it with Divine Essence.
Soon after, Sartan took to battle upon the Inferno alongside His daemonic armies to lay seige to a legion of demons that had begun an uprising against Sartan's rule over the plane. Sartan engaged the leader of the uprising, the Demon Prince Caizehl, known also as the Iron Lord, in a bloody battle across the blasted planes of the Inferno. The Iron Lord was ultimately slain by Sartan's hand and his heart ripped out and presented as a source of power for Mhaldor's new font.