Protects actin filaments from depolymerization (PubMed:15454575). Required for correct morphology of cell membranes and maturation of intercalated disks of cardiomyocytes via facilitating localization of XIRP1 and CDH2 to the termini of aligned mature cardiomyocytes (By similarity). Thereby required for correct postnatal heart development and growth regulation that is crucial for overall heart morphology and diastolic function (By similarity). Required for normal electrical conduction in the heart including formation of the infranodal ventricular conduction system and normal action potential configuration, as a result of its interaction with the cardiac ion channel components Scn5a/Nav1.5 and Kcna5/Kv1.5 (By similarity). Required for regular actin filament spacing of the paracrystalline array in both inner and outer hair cells of the cochlea, thereby required for maintenance of stereocilia morphology (By similarity). . This is the function of XIRP2 (xin actin binding repeat containing 2, ENSG00000163092).