This paper examines code-switching between English and Chinese by speakers of Chinese as a heritage language. It focuses on spontaneous, dynamic, natural and high-density code-switching within the smallest building block of a speaking turn – the turn constructional unit. Drawing upon naturally occurring, carefully transcribed data, it shows that speakers migrate between and mingle the two language systems at multiple and nested levels of phonemes, morphemes, syllable structures, tones, noun/verb phrases as well as sentence structures. It suggests that each instance of the said type of code-switching is a discursive interactional process that is accomplished through all the verbal resources from both languages that are simultaneously accessible to the speaker.