Laz is the only South Caucasian language mainly spoken outside Georgia. Its endangered status has been recognized but has not been systematically and empirically in reference to actual linguistic data (Haznedar et al. 2018). To fill this gap and to contribute to the documentation and revitalization of Laz, the morpho-syntactic properties of Laz spoken in present-day Rize (Ardeşen, Pazar and Fındıklı), were investigated. Treating Laz as a heritage language (Montrul 2016, Polinsky 2018), (baseline) Laz varieties spoken by (grand-)parental generation were contrasted with younger generation heritage speakers. To this end, one free production task and two grammatically oriented tasks were conducted. Free narratives of the Frog Story (Mayer 1969) by 73 speakers were examined in terms of the frequency counts of i) distinct content words and spatial prefixes, ii) valency alternating operations, iii) finite embedded clauses, iv) pro-dropped or scrambled clauses and iv) code-mixed utterances. Heritage speakers’ production of the relevant variables (except for code-mixing) was found to be statistically significantly lower than that of baseline speakers. Moreover, the most vulnerable aspects of Heritage Laz grammar are verbal morphology and case morphology, especially those aspects grammatically marked differently in Turkish. With ergative case being either treated as a general subject marker or dropped altogether along with structural dative case marking experiencer subjects, Heritage Laz lends support for the status of ergative as a structural case (Emgin 2009, Öztürk 2013) rather than an inherent one (Demirok 2013). Despite the extensive variation and deviation in production, the grammar of Heritage Laz turns out to be quite systematic and rule-governed, though, as heritage speakers reduce allomorphy and irregular (inflectional) morphology regulated by perceptual salience and contextual frequency (Polinsky 2018). Lastly, linguistic proficiency of speakers increases with age and the amount of time spent in rural and/or higher-altitude areas, which is in line with the endangered status of Laz. The results of the grammatically oriented tasks indicate that Heritage Laz grammar is regulated by the Principle of Transparency (Aalberse et al. 2019), exhibiting a higher level of analyticity. Heritage speakers produce analytical constructions rather than synthetic ones. The following resilience hierarchy has emerged with respect to valency alternations: Causativization with o->Higher applicativization with a->High applicatives with -u>High applicatives with i-> Benefactive Reflexives with i->Passivization > Direct object reflexives with i-. The erosion of the syncretic pre-root vowel i- provides evidence for its status as a verbal expletive, leading to a syntax-semantics mismatch and thus a violation of transparency (Eren 2021, c.f. Öztürk & Taylan 2017, Öztürk 2021). As for aspect, the root-dependency of the imperfective markers has been neutralized. The voice-dependency has been maintained, which lends further support for the preference of heritage speakers for more local syntactic dependencies, crucially in the domain of allomorphy reduction. As a result of this simplification conditioned by incipient changes in the baseline varieties and also by transfer effects from Turkish, and the emergent differentiated system conforms to the principle of one-to-one form-meaning mapping where each (transitive) aspect marker bears a distinct meaning, i.e., habituality and progressivity.