Technetium-99m hexakis-2-methoxyisobutyl isonitrile (99mTc-MIBI) distribution is flow-dependent, permitting the imaging of coronary perfusion defects. However, the behaviour of this tracer in viable and necrotic tissues within the ischaemic area at risk is still being debated. In a clinically relevant canine model, dogs were submitted either to a 24-h permanent occlusion (group 1) of the left descending coronary artery (LAD) or to a 90-min LAD occlusion followed by 22.5 h reperfusion (group 2). 99mTc-MIBI and radiolabelled microspheres were injected 3 h before sacrifice. After delimiting the area at risk and the infarct by Evans blue perfusion and triphenyltetrazolium chloride staining, heart slices were imaged by scintigraphy and tissue radioactivity measured in a gamma-counter. In the necrotic area of both groups, the 99mTc-MIBI distribution was proportional to the myocardial blood flow, approximating a 1 : 1 ratio (identity line slope 1, intercept 0) with highly significant correlation coefficients (group 1 r =0.87, group 2 r =0.86), whereas in the viable-ischaemic area of both groups, the data points are widespread above and below the identity line, indicating both over-and underestimations of blood flow in these tissue areas. These results were more pronounced following reperfusion as compared with permanent occlusion. Multiple linear regression analysis confirms differences (P <0.001) in 99mTC-MIBI distributions between the viable-ischaemic and the necrotic zones. Delineation of the ischaemic area at risk was possible only with permanent occlusion. A hypoperfused area was observed after reperfusion but differs from the anatomical infarcted area. These results indicate that the 99mTc-MIBI distribution is not significantly influenced by myocardial cell death, whereas the relationship of 99mTc-MIBI to blood flow in the remaining viable-is-* Supported by grant IU-0027, Medical Research Council of Canada ** Postdoctoral fellow of the Canadian Heart Foundation *** Bursor from the Canadian Heart Foundation Offprint requests to: J.-G. Latour chaemic myocardium salvaged by reperfusion appears more deeply affected. Therefore, the influence of tissue viability on the 99mTc-MIBI distribution in the myocardium must be reconsidered in the light of these observations.