['This study was designed to assess whether measurement of the index of microvascular resistance (IMR) could help prospectively identify patients who develop periprocedural myocardial infarction (PPMI).', 'IMR was measured in 54 patients before and following percutaneous coronary intervention (PCI) in a culprit vessel with a PressureWire using the equation IMR = Pa(Hyp) × Tmn(Hyp) (Pd(Hyp)-Pw/Pa(Hyp)-Pw). IMR was also measured in an angiographically normal reference vessel. The relative pre-IMR ratio (rPIMR) defined as IMR Culprit divided by IMR Non-Culprit was also calculated. Troponin was sequentially sampled up to 24 h following PCI. Mean troponin post-PCI was 0.37±0.8 ng/ml. 33 (61%) patients fulfilled the criteria for PPMI. IMR pre-PCI was the most significant correlate of post-PCI troponin (r=0.43 p=0.001), however, the number of balloon inflations (r=0.3, p=0.02) and rPIMR (r=0.33 p=0.017) were also correlated. IMR pre-PCI was higher in patients with periprocedural myocardial infarction compared with patients without PPMI (IMR pre-PCI 21.2±2.1 PPMI vs 15.6±1.8 No PPMI, p=0.02). The strongest predictor of troponin post-PCI was IMR pre-PCI (β 0.7, p=0.02). Both IMR pre- and rPIMR were predictive of PPMI (OR 11 (1.3 to 90.5) p=0.026, OR 1.09 (1 to 1.19) p=0.03, respectively).'] Does the index of microvascular resistance identify patients with periprocedural myocardial infarction in elective percutaneous coronary intervention?