The Unyielding Heart, also known as the Undying Heart, or simply as the Heart, was a sanctum within the main temple of the Ascendant cult that was located on the planet Bar'leth. The Ascendant used the sanctum to build inventions in their attempts to mimick the dark side of the Force. Eventually, the University of Bar'leth was built over the ruins of the temple and sanctum. The archaeologist Kho Phon Farrus traveled to the University of Bar'leth in search of the Heart in order to complete the Ascendant's Mantra and find the fabled Spark Eternal. When they arrived at the office of Sava Iglan'tine Nos, Farrus demanded Nos take them to the Heart, believing that it was a physical relic. The sava instead led to the sanctum, where she revealed to Farrus that the sanctum and Heart were in fact the same thing, and that the Spark Eteranl was already there.