BACKGROUND Syndecan-4 is a transmembrane heparan sulfate-carrying glycoprotein that mediates signal transduction pathways activated by growth factors and cell surface receptors, thereby modulating tissue regeneration, angiogenesis, and focal adhesion. The aim of the present study was to determine the clinical use of serum syndecan-4 concentration for diagnosis of heart failure. METHODS Concentration of serum syndecan-4 and other biomarkers of heart failure was measured in 45 patients with heart failure and 21 healthy subjects. Clinical and echocardiographic parameters of cardiac function were recorded. RESULTS Serum syndecan-4 concentration significantly increased in proportion to the decrease in ejection fraction (r=-0.599, p<0.001) and increase in the left ventricular (LV) mass index (r=0.315, p<0.05). Serum syndecan-4 concentration was significantly correlated with LV geometrical parameters (i.e. LV mass index, LV end-diastolic volume, and LV dimension), while B-type natriuretic peptide (BNP) was significantly correlated with pressure-related parameters [i.e. early transmitral flow velocity/early diastolic velocity of the mitral valve annulus (E/e'), right ventricular systolic pressure, and left atrial volume index]. Syndecan-4 concentration did not significantly correlate with plasma BNP, transforming growth factor-1, matrix metalloproteinase-2, and tenascin-C concentrations. Serum syndecan-4 concentration could predict cardiac death and re-hospitalization due to heart failure (area under curve, 0.706, p<0.05). CONCLUSIONS Serum syndecan-4 concentration shows promise as a novel diagnostic and prognostic biomarker for heart failure. Since syndecan-4 correlated with LV geometrical rather than hemodynamic parameters, serum syndecan-4 may represent a biomarker of LV remodeling in the failing heart.