In this study, we investigated whether the Na(+)/Ca(2+) exchanger (NCX) inhibitor SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy-5-ethoxyaniline) might have a protective effect against myocardial ischemia-reperfusion injury in rats. In particular, we focused on cardiac function using Doppler echocardiography and cardiac gene expression. We intravenously administered either SEA0400 and delivery vehicle or only the vehicle (as a control) to Wistar rats 5 min before ischemia was induced. Reperfusion was performed after 30 min of ischemia. At 1 week after ischemia-reperfusion injury, we assessed hemodynamics by inserting a polyethylene-tubing catheter, cardiac function by Doppler echocardiography, and myocardial mRNA expression was determined by Northern blot analysis. Left ventricular (LV) end-diastolic dimensions (LVDd) and LV end-diastolic volume (LVEDV) were significantly increased in the ischemia-reperfusion rat model group compared to the control group. The SEA0400-treated group had a significantly attenuated LVDd (P<0.05) and LVEDV (P<0.01) increase, compared to the vehicle-treated group. A decrease in the LV ejection fraction (P<0.05) was significantly prevented in the SEA0400-treated group compared to the vehicle-treated group. Moreover, mRNA expression of plasminogen activator inhibitor-1 in the non-infarcted LV of the SEA0400-treated group was significantly lower than in the vehicle-treated group (P<0.05). This study demonstrates that the NCX is an important mechanism for cell death in myocardial ischemia and reperfusion in rats. SEA0400 may prove to be a promising new drug in the clinical treatment of myocardial ischemia and reperfusion.