Heart blood, the blood governed by the heart, is the material basis for the physiological activities of the heart including mental activities. Propelled by heart qi, it circulates in the vessels to nourish and moisten the entire body. Since heart blood nourishes the heart, it plays a vital role in the heart governing the blood and vessels as well as housing the mind. Though the smooth flow of heart blood relies on the propelling of heart qi, abundant heart blood is a prerequisite to the regular blood circulation. Heart blood is the substantial foundation for mental activities. Because performing mental activities consumes heart blood, it will be difficult for one to think deeply and have quick-wittedness when one’s heart blood is not abundant.