Sorcin is a 22 kDa Ca²⁺ binding protein expressed in cardiac muscle. Recent studies have revealed that sorcin over-expression in cardiomyocytes leads to stimulation of sodium-calcium exchange (NCX) activity (Seidler et al, 2003). NCX expression is altered in many models of heart failure. In a recent study of a rabbit model of left ventricular dysfunction (LVD), increased NCX protein levels but decreased activity were observed (Quinn et al, 2003). The object of this study was therefore to quantitatively examine sorcin expression in this model of LVD. Eight weeks after ligation of a large branch of the circumflex coronary artery under anaesthetic (100 mg/kg of sodium pentobarbitone which was given by intravenous injection), hearts were removed after an overdose of Euthatal (1 mg/kg). Tissue from the basal region of the LV was removed, homogenised and total protein content was determined. Western blots were performed using the NuPAGE system (Invitrogen) and membranes were probed with a polyclonal antibody against sorcin (Zymed, 1:1000). Sorcin protein bands were normalised against the internal standard GAPDH. Strong signals were obtained from the dimer (44 kDa) and used to quantify sorcin expression. Immunoblot signals due to the monomer were barely detectable under these conditions. This is consistent with reports that sorcin exists as a dimer at physiological concentrations. The average optical density of the sorcin dimer in LVD was significantly lower when compared to that of sham (71.2±11.5% (SEM), P < 0.05, n = 9). No obvious changes in monomer signals were observed.These results suggest that sorcin expression is significantly reduced in this rabbit model of LVD. Decreased sorcin expression may decrease NCX activity and explain the apparent anomalous changes in expression and activity in LVD.