Chinese medicine recognizes five Yin Organs (also know as Zang organs): the Heart, Lung, Spleen, Liver and Kidney. The Zang Organs are firmer, more solid, than the fu (Yang) Organs. The Yin Organs transform, store and move the fundamental substances of the body.
The Yin Organs are thought of as being deeper inside the body. They are generally more medically important. The Pericardium is sometimes considered a sixth Yin Organ.