Following the theory of conceptual metaphor in cognitive linguistics, this paper studies a predominant conceptual metaphor in the understanding of the heart in ancient Chinese philosophy: the heart is the ruler of the body. The most important conceptual mapping of this metaphor consists in the perceived correspondence between the mental power of the heart and the political power of the ruler. The Chinese heart is traditionally regarded as the organ of thinking and reasoning, as well as feeling. As such, it is conceptualized as the central faculty of cognition. This cultural conceptualization differs fundamentally from the Western dualism that upholds the reason-emotion dichotomy, as represented by the binary contrast between mind and heart in particular, and mind and body in general. It is found that the heart as ruler metaphor has a mirror image, namely the ruler is the heart of the country. The ruler as the "heart" of the country leads his nation while guided by his own heart as the "ruler" of his body. It is argued that the two-way metaphorical mappings are based on the overarching beliefs of ancient Chinese philosophy in the unity and correspondence between the microcosm of man and the macrocosm of universe. It is suggested that the conceptualization of the heart in ancient Chinese philosophy, which is basically metaphorical in nature, is still spread widely across Chinese culture today. (Ning Yu)