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We have evaluated left ventricular ejection fraction (LVEF) at rest (REF) and after stress (SEF) with dual-isotope gated myocardial perfusion SPECT (GMPS) with 201Tl injected at rest and 99mTc sestamibi (99mTc-MIBI) injected at peak stress, to assess the occurrence of post-stress stunning.Two hundred and thirty-six consecutive patients had GMPS at rest and post-stress. The summed stress and rest scores and the summed difference score (SDS) were calculated using a 17-segment model analysis of GMPS. An SDS >3 indicated significant ischaemia. The REF and SEF were automatically generated and the DEF (SEF-REF) was calculated.Significant stress induced ischaemia was observed in 103 patients (44%). REF was 54.72%±15.75% and SEF was 55.69%±16.65% (P<0.0015). DEF was −2.25±5.36 and 3.42±5.25 in patients with and without ischaemia, respectively (P<0.001). Post-stress stunning (>5% decrease in LVEF) was present in 68 patients (29%) and in 58/103 (56%) patients with ischaemia, after treadmill exercise or dipyridamole infusion and was more common in patients with severe ischaemia. The single significant predictor of DEF in univariate analysis and of stunning using logistic binary regression was stress induced ischaemia (P<0.0001).LVEF increases post-stress in patients with no ischaemia and may decrease in 56% of patients with ischaemia, possibly due to stunning. The best predictor of post-stress stunning is stress induced ischaemia and its occurrence is related to the degree of ischaemia.