In Tedim Chin 'heart' idioms, the metonymy and the metaphor are joined together. Tedim Chin speakers believe the heart stands for emotion, personality, and oneness, etc. Out ofthese metonymies, the metaphoric usages are built up. Thus, a 'hard heart' is stubbom, a heart flies when it yeams for someone, and a heart joined together is to be one spirit. These processes are activated at a single point of time in the psycho-cognitive mind of the Tedim Chin speakers. As David Tuggy (1994, p.c.) has said "Thus language is conventionalized, each linguistic unit can be easily activated as a whole, though it may be intrinsically complex". This study is related to the fields of prototype effect, and to the semantic continuum of idioms. These fields of study are helpful in deciding which lexical entities to include in a dictionary. They are also helpful for understanding the peoples' emic worldview from the sociological, anthropological, and cultural points of view. (Khoi Lam thang)