The aim of this study was to investigate the dose-dependent effect of pretreatment with the selective sodium-hydrogen exchange NHE-subtype 1 inhibitor cariporide on myocardial infarct mass in a rabbit model of coronary ligation and reperfusion. Furthermore, in a second part of the study, we tested the effect of cariporide in the rabbits when given prior to reperfusion. Rabbits (n=49) were randomized in 7 groups: saline vehicle, cariporide: 0.01, 0.03, 0.1 and 0.3 mg/kg, and subjected to a 30 min occlusion of a branch of the left coronary artery followed by 2 h reperfusion. Cariporide was given as a bolus intravenously 10 min before occlusion or 5 min before reperfusion. After reperfusion, myocardial infarct mass was determined by triphenyl tetrazolium chloride staining and expressed as a percent of area at risk. Cariporide given intravenously 10 min before occlusion in doses of 0.01, 0.03, 0.1, 0.3 mg/kg, led to a dose-dependent reduction in infarct mass from 58+/-6% in controls to 48+/-4% (-17%, NS), 36+/-5% (-38%, p<0.05), 26+/-6% (-55%, p<0.05), 11+/-4% (-81%, p<0.05) respectively, whereas area at risk did not differ in between the groups. The effect of the lowest dose of 0.01 mg/kg did not reach significance. Plasma levels at different doses of cariporide were correlated to the respective infarct mass. After coronary occlusion left ventricular end-diastolic pressure (LVEDP) significantly increased throughout occlusion and reperfusion. Cariporide in the doses of 0.3, 0.1 and 0.03 mg/kg normalized LVEDP when measured after 2 h reperfusion. In controls hemodynamic parameters such as mean arterial blood pressure (MAP), heart rate (HR), left ventricular pressure (LVP) and LV dP/dt(max) were not significantly changed by ischemia/reperfusion with the exception of MAP, LVP and LV dP/dt(max) which were significantly decreased after 120 min reperfusion. Cariporide at doses of 0.1, 0.03 and 0.01 mg/kg did not significantly influence these parameters, whereas the highest dose of 0.3 mg/kg prevented the decrease of MAP and LVP. Cariporide (0.3 mg/kg i.v.) administered 5 min before reperfusion significantly reduced infarct mass by 31%. Under these conditions the increase of LVEDP after coronary occlusion was not influenced by cariporide. As in the pretreatment experiments, the decrease of MAP and LVP was prevented when measured 2 h after reperfusion. The results show that pretreatment with the NHE-subtype 1 inhibitor cariporide is cardioprotective by reducing infarct mass in rabbits in a dose-dependent manner. While the cardioprotective effect of pretreatment could be demonstrated over a broad range of doses, the efficacy of the compound when given only on reperfusion was significant but more limited.