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Abstract Neonatal dilated cardiomyopathy (DCM) is a poorly understood muscular disease of the heart. Several homozygous biallelic variants in LMOD2, the gene encoding the actin-binding protein Leiomodin 2, have been identified to result in severe DCM. Collectively, LMOD2-related cardiomyopathies present with cardiac dilation and decreased heart contractility, often resulting in neonatal death. Thus, it is evident that Lmod2 is essential to normal human cardiac muscle function. This study aimed to understand the underlying pathophysiology and signaling pathways related to the first reported LMOD2 variant (c.1193 G > A, p.Trp398*). Using patient-specific human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and a mouse model harboring the homologous mutation to the patient, we discovered dysregulated actin-thin filament lengths, altered contractility and calcium handling properties, as well as alterations in the serum response factor (SRF)-dependent signaling pathway. These findings reveal that LMOD2 may be regulating SRF activity in an actin-dependent manner and provide a potential new strategy for the development of biologically active molecules to target LMOD2-related cardiomyopathies.