This study investigates the use of overt and null subjects in Bulgarian in child heritage speakers with L2 German. The alternation of overt and null pronominal subjects in null-subject languages like Bulgarian depends on grammatical and discourse conditions and contrasts with German. Oral narratives were elicited in Bulgarian, comparing the performance of the heritage children to that of monolingual children and adults. Overall 68 Bulgarian narratives of 39 speakers were analysed as to the use of overt and null pronominal subjects in topic-continuity and topic-shift contexts. The results reveal similar subject realisation for all speakers, supporting early acquisition of null-subject grammars. Analyses of topic-continuity and -shift contexts showed similar overall patterns in children's and adults' subject use, with children producing somewhat more overt subjects in topic-continuity and ambiguous overt pronouns in topic-shift contexts than adults. However, the bilinguals used significantly more ambiguous null subjects than monolinguals. These results suggest that fine-grained discourse constraints of null-subject grammars are more difficult for bilinguals to acquire and maintain. The near adult-like performance of the bilinguals in some contexts can be attributed to the fact that most of them were Bulgarian-dominant and received non-attrited parental input. Differences are also attributable to cross-linguistic influence.