Inclusion Criteria: * Pathogenic or likely pathogenic mutation in BAG3 * Medical history of diagnosis of DCM * Stable combination of HF SoC medications * Adequate acoustic windows for echocardiography Exclusion Criteria: * Presence of antibodies to AAV9 * Presence of a pathogenic or likely pathogenic variant in another gene where that other gene is authoritatively recognized as causal for DCM. * Decompensated HF Note: Other inclusion and exclusion criteria may apply.