The heart is called the 'King' of the organs. The Internal Medicine Classic states: 'The heart commands all of the organs and viscera, houses the spirit, and controls the emotions.' In Chinese, the word for 'heart' (xin) is also used to denote 'mind'. When the heart is strong and steady, it controls the emotions; when it is weak and wavering, the emotions rebel and prey upon the heart mind, which then loses its command over the body.
Physiologically, the heart controls the circulation and distribution of blood, and therefore all the other organs depend upon it for sustenance. Thoughts and emotions influence the function of various organs via pulse and blood pressure, which are controlled by the heart, where emotions arise.
Internally, the heart is functionally associated with the thymus gland, which is located in the same cavity and forms a mainstay of the immune system. Extreme emotions such as grief and anger have an immediate suppressive effect on the immune system by inhibiting thymus function, a phenomenon that has long been observed but little understood in Western medicine.
Externally, the heart is related to the tongue, to which it is connected by the heart muscle. The color and texture of the tongue thus reflect the condition of the heart. Speech impediments such as stuttering and mutism are often caused by dysfunction or imbalance in heart energy. Facial complexion, which is a direct reflection of blood circulation, is also a major external indicator of heart function. Fire energy makes the heart the dominant organ of summer, during which season the heart must increase circulation to the surface in order to dissipate excess body heat.
Passage without points
The meridian originates from its pertaining organ the heart passes through the diaphragm connects with the small intestine. The branch from the heart runs alongside the esophagus reaches the face to connect with the eye.
Passage with points
The branch from the heart goes upward to the lung turns downward and emerges from the axilla (HT 1) from there goes along the posterior border of the medial aspect of the arm down to the cubital fossa continues to descend along the posterior border of the medial aspect of the forearm to the pisiform region enters the palm follows the radial side of the little finger ends at its tip (HT 9), where it links with the small intestine meridian.
The hand lesser Yin (Shaoyin) heart meridian starts in the heart, emerg¬ing through the blood vessels surrounding this organ. Traveling downward, it passes through the diaphragm to net the small intestine. Another branch separates from the heart, traveling upward along the side of the esophagus to meet the tissues surrounding the eye. A further meridian separates from the heart, travels directly up into the lung, and then veers downwards to emerge below the axilla. It travels down the medial aspect of the upper arm, medial to the hand greater Yin (Taiyin) lung and hand reverting Yin (Jueyin) pericardium meridians, and passes over the antecubital fossa. It continues down the anteromedial margin of the forearm to the capital bone on the wrist, travelling along the radial side of the fifth metacarpal bone to terminate at the tip of the little finger