Background: The molecular mechanisms involved in development of heart failure are only partially known. We previously found increased expression of all four members of the syndecan family in the non-infarcted region of failing mouse hearts. The syndecans are co-receptors for several growth factors such as fibroblast growth factor (FGF)-2 and involved in cell-extracellular matrix communication. The aim of this study was to examine regulation of syndecan-4 in cardiac cells and to assess its role in regulation of á-skeletal actin synthesis.Methods: Cardiomyocytes and fibroblasts were isolated from neonatal mice and treated with tumor necrosis factor (TNF)-á, FGF-2, leukemia inhibitory factor (LIF) or activin-A and TNF-á, FGF-2, LIF, activin A, interleukin (IL)-1â, endothelin-1 or interleukin (IL)-18, respectively. Cardiomyocytes and fibroblasts isolated from neonatal syndecan-4 knock-out mice and wild-type mice were treated with FGF-2. The mRNA levels of á-skeletal actin and syndecan-4 were assessed by real-time PCR. Results: Electron microscopy showed that the cardiomyocyte cultures contained 92% cardiomyocytes and that the fibroblast cultures were almost 100% pure. The expression of syndecan-4 was significantly increased following stimulation with LIF and TNF-á in cardiomyocytes, and following stimulation with IL-1â and TNF-á in fibroblasts. The expression of á-skeletal actin was significantly lower in FGF-2-stimulated knock-out cardiomyocytes compared to FGF-2-stimulated wild-type cardiomyocytes. Conclusion: We have established a protocol for isolation of cardiac myocytes and fibroblasts from neonatal mice, and found that LIF and TNF-á caused significant up-regulation of syndecan-4 in cardiomyocytes, while IL-1â and TNF-á increased the expression in fibroblasts. Syndecan-4 was shown to regulate synthesis of á-skeletal actin, which suggests that syndecan-4 might be involved in the pathogenesis of heart failure.