A. During cardiac development, TBX5 activates transcription of relevant downstream targets, including cardiomyocyte structural genes. At non-cardiac targets, TBX5 recruits the NuRD chromatin remodeling complex to inhibit lineage-inappropriate gene expression. Together, these functions allow for proper development and septation of the heart. B. Disruption of the TBX5-NuRD interaction (yellow star), either through disease mutations or evolutionary mechanisms, derepresses targets of TBX5-mediated repression, leading to congenital heart defects such as AVSDs.