The nature and extent of the impact of language transfer in majority–minority language contexts have been widely debated in both second- and heritage-language acquisition. This study examines four linguistic areas in three oral narratives collected from Egyptian and Palestinian heritage speakers in the United States (namely, plural and dual morphology, possessive constructions, and restrictive relative clauses), with a special focus on how the second language (English) influences the structure and use of these areas in connected discourse. In addition, the study examines the relationship between second-language transfer and the incompleteness and attrition of heritage Arabic. The findings show that heritage speakers have various gaps in their knowledge of the examined areas, particularly in forms and patterns that diverge from their counterparts in their dominant L2. The results also suggest that transfer effects are restricted to specific forms that are marked (e.g. broken plurals), infrequent (duals), or characterized by processing difficulty (as seems to be the case with the dependencies in the relative clauses). Moreover, transfer effects are intimately related to both the attrition and incomplete acquisition of the speakers’ knowledge of the four areas under study. The implications of the study for heritage language research are discussed.