GGsTop is a highly potent and specific, and irreversible γ-glutamyl transpeptidase (GGT) inhibitor without any influence on glutamine amidotransferases. The aim of the present study was to investigate the involvement of GGT in ischemia/reperfusion-induced cardiac dysfunction by assessing the effects of a treatment with GGsTop. Using a Langendorff apparatus, excised rat hearts underwent 40 min of global ischemia without irrigation and then 30 min of reperfusion. GGT activity was markedly increased in cardiac tissues exposed to ischemia, and was inhibited by the treatment with GGsTop. Exacerbation of cardiac functional parameters caused by ischemia and reperfusion, namely the reduction of left ventricular (LV) developed pressure and the maximum and negative minimum values of the first derivative of LV pressure, and the increment in LV end-diastolic pressure was significantly attenuated by GGsTop treatment. The treatment with GGsTop suppressed excessive norepinephrine release in the coronary perfusate, a marker for myocardial dysfunction, after ischemia/reperfusion. In addition, oxidative stress indicators in myocardium, including superoxide and malondialdehyde, after ischemia/reperfusion were significantly low in the presence of GGsTop. These observations demonstrate that enhanced GGT activity contributes to cardiac damage after myocardial ischemia/reperfusion, possibly via increased oxidative stress and subsequent norepinephrine overflow. GGT inhibitors have potential as a therapeutic strategy to prevent myocardial ischemia/reperfusion injury in vivo .