The heart is situated in the chest, above the Diaphragm, and is enveloped by pericardium externally. TCM believes that the heart governs all the other zang- fu organs and, therefore, is a "monarch organ". The heart, pertaining to fire in the five elements, consists of heart-yin, the material structures containing the heart-blood, and heart- yang, the functional activities. As for physiological functions, the heart is thought to, first, dominate blood and vessels since it is the motive force for blood circulation. The blood vessels are the physical structures containing the blood. The blood vessels are linked with the heart to form a closed system, and blood circulation is performed by the cooperation of the heart and the blood vessels. Under the impulse of heart-qi, blood is transported to all parts of the body fot nutritive purpose.

Thereby the condition of heart-qi and the blood volume rmay be shown in both the pulse condition and the complexion. That's why Basis Questions (Su Wen) says, "The beart has its outward manifestation in the face or complexion". As a result, whether heart-qi and heart-blood are sufficient or not can affect the strength, rate and rhythm of the heart.

The heart houses the mind, also known as the heart dominating the mental activities. The mind, in its broad meaning, refers to the outward manifestations of the life activities of the whole body, and, in its narrow sense, to mental activities controlled by the heart, including consciousness, spirit, thinking, etc. The zang - fu theory holds that mental activities and thinking are to take the heart's functions as their basis. Spirit, consciousness, thinking, memory and sleep are all related to the function of the heart in housing the mind. Therefore, Miraculous Pivot (Ling Shu) says, "The heart is the residence of the mind" and also, "The heart takes on the performance of activities." The heart opens into the tongue. "Resuscitation", in TCM, means the close relationship between a particular zang-organ and one of the sense organs in the structure, physiology and pathology.  So the heart, though being in the body, is connected with the tongue by the heart-meridians. Through such a connection, whether the heart functions normally or not can be clearly learnt from the tongue condition. In other words, the tongue condition may show the physiological and pathological changes of the heart. So TCM holds: "The tongue serves as the mirror (or body opening) of the heart". In addition, the heart has its outward manifestations in the face. The heart corresponds to joy in the emotions. And its meridians connect with the small intestine with which they are internally-externally related.

Appendix; Pericardium

The pericardium, serving as the peripheral tissue surrounding the heart, plays a part in protecting the heart. When exogenous pathogenic factors attack the heart, the pericardium is always the first to be attacked. The heart, if invaded by the pathogens, will be impaired and diseases will ensue. For example, high fever, coma and red tongue are described as "heat-pathogen attacking the pericardium," and, in fact, the clinical manifestations of the pericardium invaded by exogenous pathogens are the same as those of the heart. For this reason, the pericardium is usually regarded as an attachment to the heart.

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