The heart plays a crucial role in the human body as the master and controller of human activities, coordinating the functions of other internal organs. The heart is responsible for various parts of the body, which is why there is a Chinese saying that "The heart is the master of the five viscera and the six bowels." The pericardium forms the external defense of the heart, so when a pathogenic energy attacks the heart, it must pass through the pericardium first, resulting in symptoms of a diseased pericardium, such as high fever, coma, and delirium.
The heart is also the master of the spirits, including mental conditions, consciousness, and thought. Therefore, when the heart is diseased, related activities will be disordered, leading to symptoms such as insomnia, forgetfulness, and mental confusion. The heart is the master of the blood vessels, and its glory is manifested in the face, with blood vessels being the channels through which blood circulates. The pushing power of the heart is responsible for the circulation of blood, and the Chinese believe that when energy circulates smoothly, blood will also circulate smoothly. A person's complexion reflects the condition of the heart, and a healthy heart will manifest a shiny and reddish complexion with high spirits.
The tongue is the outlet of the heart, and the heart extends its energy to the tongue. Therefore, when the heart is in harmony, the tongue will be able to differentiate different flavors, reflecting the close relationship between the heart and the tongue. A disease of the heart will be manifested in the tongue, and different tongue conditions can indicate various heart issues. Two Chinese phrases often mentioned in relation to the heart are "the heart with its cavity in the tongue" and "the tongue as the seedling of the heart."