Conversely to plenty of studies describing how L1 transfer affects L2 systems, where the two grammars, L1/L2, often only come to interact later in life, less is known of dominant language transfer in heritage language grammars. Unlike in L2 speakers, the dominant language of the heritage speaker potentially affects its weaker language already from childhood. Evidence of dominant language transfer, however, exists in language production studies focusing on syntax. Therefore, an oral structural priming task was employed to compare transfer effects in advanced Swedish speakers of Italian and early heritage Italian speakers dominant in Swedish. Intrinsic to this comparison is the Basic Continuity hypothesis (Romano 2018), which proposes that highly proficient L2 speakers integrate semantic and syntactic information relevant to an L2 property lacking in the L1 in native-like ways. Results showed that heritage and L2 grammars are similarly impervious to transfer effects and coordinate structural and lexico-semantic information in native-like ways, consistent with the Basic Continuity. Divergence from native controls is shown to be remarkably compatible with monolingual grammars at earlier developmental stages.