Numerous studies have examined the effect of Na(+)/H(+) exchanger (NHE) inhibition on the myocardium; however, the effect of NHE-1 inhibition on neutrophil function has not been adequately examined. An in vivo canine model of myocardial ischemia-reperfusion injury in which 60 min of left anterior descending coronary artery occlusion followed by 3 h of reperfusion was used to examine the effect of NHE-1 inhibition on infarct size (IS) and neutrophil function. BIIB-513, a selective inhibitor of NHE-1, was infused before ischemia. IS was expressed as a percentage of area at risk (IS/AAR). NHE-1 inhibition significantly reduced IS/AAR and reduced neutrophil accumulation in the ischemic myocardium. NHE-1 inhibition attenuated both phorbol 12-myristate 13-acetate- and platelet-activating factor-induced neutrophil respiratory burst but not CD18 upregulation. Furthermore, NHE-1 inhibition directly protected cardiomyocytes against metabolic inhibition-induced lactate dehydrogenase release and hypercontracture. This study provides evidence that the cardioprotection induced by NHE-1 inhibition is likely due to specific protection of cardiomyocytes and attenuation of neutrophil activity.