The Heart's main function in Chinese Medicine is to control the flow of Blood, the Blood Vessels and to house 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.
A Heart Deficiency has both physical and psychological effects. Physically speaking, in the case of Heart Qi or Blood Deficiency typical symptoms include low energy, palpitations, shortness of breath, night sweats or fainting.
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 leading to depression, anxiety, insomnia or a high level of irritability.
Very much like in Western medicine, the Heart regulates Blood circulation in the vessels, tissues and Organs. That being said in Chinese Medicine other Organs, such as the Lungs, Spleen and Liver, also participate in Blood circulation. When Heart Qi or Blood is Deficient, Blood circulation is weak. A typical symptom is that hands and feet get cold.
Heart-Blood also impacts menstruation in several ways as it descend to the Uterus to promote the discharge of menstrual Blood (also called Tian Gui) and more generally nourishes the Uterus. Heart-Blood conditions can directly cause period-related disorders. For instance Heart-Blood deficiency may cause amenorrhoea, Heart-Blood Heat may cause menorrhagia and Heart-Blood Stagnation may cause painful periods.
Lastly 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 Channel, so any Heart condition will be reflected by the tongue's color, 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, is bright and has a normal shape. The sense of taste works properly as well. If Heart Blood or Qi are Deficient the tongue is pale and white with a thin shape. When Heart Blood or Qi are Stagnant, the tongue is dark purple and ecchymoses appear. If Heart Heat is Excessive, the tongue could be red and with painful tongue ulcers.
Blood and Body Fluids mutually exchange with each other. Body Fluids 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 avoid activities that make them sweat heavily because it will deplete the Blood even further. This can cause a shortness of breath and heavy heartbeats.