To evaluate the utility of 99mTc-labeled nitroimidazole (BMS) in the detection of ischemic or reperfused myocardium, we performed dual-tracer autoradiography with BMS and [125I]iodoantipyrine (IAP). METHODS In open-chest rats, the left coronary artery was ligated to produce 15- or 60-min ischemia followed by reperfusion or 60-min ischemia without reperfusion. BMS was injected just before ligation, 1 min before reperfusion or 15 min after reperfusion. RESULTS In the area at risk, regional myocardial blood flow (rMBF) evaluated by IAP recovered to the level in the nonischemic septum in all hearts, except in 60-min occlusion without reperfusion. In myocardium reperfused after 15-min ischemia (stunned), normalized BMS uptake (%BMS) in the area at risk was significantly increased only when BMS was injected before ischemia. When BMS was injected before 60-min ischemia or just before reperfusion, %BMS was significantly higher at the marginal zone of infarction than in the infarcted area. In contrast, %BMS was significantly lower in the infarcted area when BMS was injected during reperfusion. After 60 min of occlusion without reperfusion (permanent occlusion), rMBF in the area at risk was significantly decreased as was %BMS. In the peripheral zone of the area at risk, rMBF was significantly reduced, but %BMS was significantly increased. CONCLUSIONS BMS images stunned myocardium only when it is injected before ischemia, while it images the area at risk subjected to prolonged ischemia when it is injected up to the time of reperfusion. The infarcted area can be negatively visualized when BMS is injected after reperfusion.