The Heart of Heaven is located at the center of the Seven Capital Cities of Heaven, and only appears once every eighty-eight years
Points of Interest
Since the Heart of Heaven is formed when each of the seven cities occupy the same plane of existence, it has aspects of each city as well as Earth
The Heart of Heaven is a palace comprised of different aspects of the Seven Capital Cities of Heaven and Earth, so if one should break the borders of the palace, they could end up almost anywhere
Immortal Iron Fist #8 (2007)
Once every eighty-eight years, during a heavenly convergence, each of the Seven Capital Cities of Heaven occupy the same space and time to create a place called the Heart of Heaven. It is at this time that each of these cities brings together their Immortal Weapons to do combat in a tournament for the right to earn a spot on the Earthly realm. The winner's city can appear on Earth once every decade while the losing cities only appear once every five decades. The Heart of Heaven is a palace with aspects of every city that make it up and includes aspects of Earth as well. The palace is unlike any place any have ever been to, and has rules and laws only unto itself. The Heart is the starting place for each match in the tournament, but if the combatants break the borders of the palace, they could end up fighting almost anywhere else.
The Heart of Heaven, just as each of the seven cities, was threatened when the terrorist group known as Hydra, under the leadership of a man named Xao, promised to destroy the ancient city of K'un-Lun. Each City's champion decided to fight together in order to defend their civilization's right to exist. The Immortal Weapons drove back Hydra and Xao's plans were ruined. A winner of the tournament was never declared, but it can be assumed the Heart of Heaven will return in another eighty-eight years to begin the tournament again.