The Heart's main function in Chinese Medicine is to control the flow of Blood, the Blood vessels and houses the Spirit/ Mind (Shen - 神). The Heart is considered to be the most important of all the Internal Organs. It is referred as the "Emperor", ruling all the Organs.
According to TCM, the Heart 'opens' into the tongue, one of the body's 'orifices'. Therefore, a TCM doctor can judge the Heart's condition by examining a patient's tongue color, form and appearance.
Psychologically the Heart houses the Mind and has an impact on the Emotion of Joy. Therefore, a Heart disease may cause the Mind to behave abnormally, such as depression, anxiety, insomnia, a high level of irritability or night sweats.
Very much like in Western medicine, the Heart regulates Blood circulation in the vessels, tissues and Organs. Although, in Chinese Medicine, other Organs, such as the Lungs, Spleen and Liver, also participate in the Blood circulation.When Heart Qi or Blood is Deficient, Blood circulation is weak. Thus the hands and feet get cold.
Heart Blood also impacts menstruation indirectly, despite that Liver Blood is the most important for the menstrual function. It is because the Heart controls the Blood releasing during menstruation. The heart is also the place where the Grain Qi (Food Qi) from the Spleen is transformed into Blood.
Strong Heart and sufficient Blood results in balanced mental activity, healthy emotional life, clear consciousness, strong memory, sharp thinking, and smooth sleep. However, if the Heart is weak and Blood is inadequate, mental activities are disturbed. Symptoms such as mental uneasiness and distress, insanity, abnormal behavior, excessive dreaming or insomnia, anxiety, and depression can appear.
The face is rich in Blood vessels, which are controlled by the Heart. Therefore, the Spirit /Mind (Shen－神）is shown in the face through its sheen and color. If the Heart is strong and Blood is sufficient, the face has a normal color with luster and moisture.
According to TCM, the tongue is connected to the Heart through the Heart Meridians, so the Heart conditions could be reflected by the tongue's colour, form and appearance, especially the tip of tongue. The sense of taste is also controlled by the Heart.
If the Heart functions properly, the tongue has a regular pale-red color, bright and have a normal shape. The sense of taste works properly as well. If the Heart function is not normal, Blood or Qi is Deficient and the tongue is pale and white with a thin shape. When Blood or Qi is Stagnated, the tongue is dark purple and ecchymoses appear. If Heart Heat is Excessive, the tongue could be red and has painful tongue ulcers.
Blood and Body Fluids mutually exchange with each other. Body Fluids will enter Blood vessels to dilute the Blood if it is too thick. Since one of the Body Fluids is sweat, someone who is Deficient in Blood should not sweat heavily because it will consume the Blood further. This can cause a short breath and heavy heartbeats. Heart Yang Deficiency can cause sweating, while Heart Yin Deficiency causes night time sweating.