Sodium channel mutations near the IQ and EFL motifs in the carboxyterminal (CT) domain have been linked to long QT (LQTS) and Brugada syndromes (BrS). IQ-calmodulin (CaM) interaction is important for regulation of cardiac Na channels. The aim of this study was to assess the role of Na+–Ca2+/CaM signaling via IQ motif of the Na+ channels in development and maturation of intercalated disc (ID). We studied transgenic mice with alanines knocked into IQ positions in the Nav1.5 CT. The homozygous mice are embryonic lethal and heterozygous mice (IQ/AA+/− mice), develop cardiomyopathy (DCM). We measured the signal and distribution of Nav1.5, syntrophin, Cx43 and ryanodine in 3 and 9 month old IQ/AA+/− mice. Results were compared to those obtained from age matched wild type mice. By immunohistochemistry we show that Nav1.5 protein in 9 month-old IQ/AA+/− mice is significantly reduced at the ID. Syntrophin that traffics Na channels to the membrane, is not altered. Cx43 which is co-located with Nav1.5 at the ID, is significantly reduced. The expression of these proteins were not altered in 3 month-old IQ/AA+/− mice. We also assessed the implication of IQ domain on the localization of Ca2+ handling protein such as ryanodine receptor and found that it was significantly altered in 9 month-old IQ/AA+/− mice. The data suggest that enhanced late INa,L in IQ/AA+/− mice contributes to DCM via remodeling of electrical and junctional proteins and demonstrate a dynamic interplay of Na+–Ca2+/CaM signaling via IQ motif of the Na+ channels in ID development and maturation. Our study highlights the importance of Ca2+/CaM-mediated regulation of Na+ channels in DCM and arrhythmia.