Heart is heat in six qi, not fire.

Huangdi Neijing. The statement that the center of six qi is heat rather than fire comes from Huangdi Neijing. Huangdi Neijing is the earliest medical classic in China and one of the four classic works of traditional medicine. The content of this book is very extensive. Besides medical theory, it also records the knowledge and achievements of ancient philosophy, astronomy, meteorology, phenology, biology, geography, mathematics, sociology, psychology, temperament and other disciplines, and permeates these knowledge and achievements into medical theory, thus making this book a multidisciplinary work with medicine as the main body, which has always been valued by doctors and experts in related disciplines and has become a research achievement in academic circles at home and abroad.