Diabetes mellitus (DM) is a chronic metabolic disorder accompanied by an increase in oxidative stress. Ischaemia-reperfusion (IR) injury is a cascade of events initiated by tissue ischaemia. The cellular damage produced by reperfusion leads to an active inflammatory response. Erythrocyte deformability and plasma viscosity are of crucial importance for the perfusion of tissues and organs. The aim of this study was to evaluate the effect of levosimendan on erythrocyte deformability during IR myocardial injury in diabetic rats.