The Heart of the Sky is the Nausicaan afterlife. The race believes that when they die, their tegol is brought to the Heart of the Sky, where the Four Winds, as well as their friends and family, dwell.

In 2377, Savonigar believed he could feel his tegol leaving his body and soar to the Heart of the Sky, where his ancestors were waiting for him. (DS9 novel: Warpath)