- "The new Heart of Lorkhan will be completed. And it will power my city for all eternity.'" — Sotha Sil
The Mechanical Heart, also referred to as the new Heart of Lorkhan, is a mechanical replication of the Heart of Lorkhan created by Sotha Sil. It first began development shortly after the events that occurred in 2E 882, where Dagoth Ur awakened and then ambushed and nearly killed the Tribunal during their annual pilgrimage to Red Mountain to renew their divine powers. The event resulted in the Tribunal being cut off from access to the Heart of Lorkhan, and the Mechanical Heart would as a response begin development as a backup to the loss of the original Heart of Lorkhan.
The Mechanical Heart was stored and would be developed in heavy security deep within the Clockwork City. He stored it within the Chamber of Lorkhan, located deep in the Clockwork City's Cogitum Centralis. The Cogitum Centalis contained an automated defense system controlled by a master factotum.
In the Mechanical Heart's early stages of development, it proved to be dangerously unstable, and Sotha Sil devised a plan to contain it as it threatened to destroy the entirety of his Clockwork City. With the creation of his own variant of Kagrenac's Tools, he was able to control the heart, and even shape or dismantle it if necessary. His plans would be rushed, as in 3E 427, the goddess Almalexia, having been driven mad by her loss of immortality, manipulated the Nerevarine to retrieve Barilzar's Mazed Band, which she used to travel to the Clockwork City to murder Sotha Sil in cold blood. He knew that one day his friend Almalexia may come to kill him, and in his final moments, attempted to ensure that his City would live on after his death. He was successful in sealing the Heart within the Chamber of Lorkhan, and his machines began finishing the construction of the Heart within it.
The Mechanical Heart was completed in 4E 200, approximately 649 years after it was first conceived and 207 years after Sotha Sil's death. Sotha Sil's creations previously required his presence, with the city's functions going into a slumbering mode in his absence. His presence was no longer needed as the heart continued to power the city and sustain its inhabitants even after his demise. The Heart also allowed the realm to find new life, as the city had been overrun with vibrant flora, with vines covering the clockwork architecture and various plant life even piercing out of various buildings in the city's landscape, possibly making the Everwound Wellspring obsolete.
It is unknown what happened to the Mechanical Heart, but stories say that the Forgotten Hero ventured into the Clockwork City and defeated the former Clockwork Apostle, Mecinar, but the stories differ from there. Some claim that the Forgotten Hero destroyed the heart in order to cut Mecinar's divine power to fight on equal ground, and the city ceased functions and the city's inhabitants were forced to abandon the city. Others claim that the hero used the Heart to harness its power and fought Mecinar on equal ground, and the Heart would live on, along with the city. The Heart was too much for the hero to handle and was disintegrated, with the hero's consciousness living on within the city. 
- Events that occur in the mission The Red Mountain in Return to Clockwork City
- Aios' dialogue in ESO: Clockwork City
- Sotha Sil's dialogue in the mission The Tools in Return to Clockwork City
- Sotha Sil's dialogue in the mission The Last Stand in Return to Clockwork City
- Luciana Pullo' dialogue in the ESO: Clockwork City
- Kellen's dialogue in the mission The City Falls in Return to Clockwork City
- Kellen's dialogue in the mission Journey's End in Return to Clockwork City
- Events of Return to Clockwork City
- Return to Clockwork City story in Legends