Biomechanical stimuli and extracellular matrix cues are important initiators for the cardiac remodeling process, and signaling hubs in the sarcolemma are important contact points between the extracellular space and cell interior, sensing and transducing biomechanical signals into a cellular response. The transmembrane proteoglycan syndecan-4 localizes to these attachment points and has been shown important in initial stages of cardiac remodeling. The objective of this study was to map the cardiac interactome of syndecan-4 to better understand its function and downstream signaling mechanisms. By combining two different affinity purification methods with mass spectrometry, we identified the cardiac syndecan-4 interactome to consist of 21 novel and 31 previously described interaction partners. 12of the novel partners were further validated to bind syndecan-4 in HEK293 (MPP7, PARVB, CCT5, CDK9, EIF22S1, PFKM, RASIP, EIF4B, PTRF/CAVIN1, AP3D1, EPB4.1 and MLP/CSRP3). 19 of the interactome partners bound differently to syndecan-4 in left ventricle lysate from aorta banded hypertrophic failing (ABHF) rats. One of these partners was the well-known mechanotransducer MLP, which showed a direct and significant increased binding to syndecan-4 in ABHF. Nuclear translocation is important in MLP mediated signalling and we found less MLP in nuclear enriched fractions from syndecan-4-/- mouse left ventricles, but an increase in nuclear MLP when syndecan-4 was overexpressed in a cardiomyocyte cell line. In the presence of a cell-permeable syndecan-4-MLP disruptor peptide, the nuclear MLP level was significantly reduced. This suggests syndecan-4 to be a mediator of nuclear translocation of MLP in the heart.