Loss of language-specific morphosyntactic structures, as well as the lexicon, is a hallmark of a `heritage language.' Specific to Russian, previous research suggested the lexicalization of grammatical aspect. This study investigated early stages of attrition in bilingual children with Russian as L1, using the narrative retelling paradigm. Narratives of 15 Russian-English bilingual subjects, between the ages of 4;0 and 10;11, were examined for signs of possible grammatical aspect restructuring as well as language-specific case and agreement errors. Fifteen monolingual Russian-speaking children within the same age range were tested in Moscow using the same methodology. Our results show only a few aspectual errors contextually, but none in morphological devices, among bilingual children. However, we found numerous lexical errors, as well as errors in the domain of morphosyntax. We conclude that L1 attrition takes place selectively with grammatical aspect spared in the initial process. An inverse correlation was found between the number of produced errors and the length of uninterrupted L1. Our results also suggest that consistent use of Russian at home and in extra-curricular activities, in addition to the length of uninterrupted L1, slows down the attrition of one's native language, especially in the presence of the dominant L2 language.