The extent of coronary microvascular dysfunction might be related, not only to patient characteristics and procedural factors, but also to the inflammatory status. The aim of the present study was to examine a possible association between inflammation, as reflected by the serum C-reactive protein (CRP) levels, and the extent of baseline and post-percutaneous coronary intervention (PCI) coronary microvascular dysfunction in patients with non-ST-segment elevation acute coronary syndrome undergoing PCI. A total of 42 patients undergoing PCI for non-ST-segment elevation acute coronary syndrome were enrolled. Coronary microvascular resistance (MR) was determined in the territory of culprit artery using a Doppler probe- and a pressure sensor-equipped guidewire both before (taking the collateral blood into account) and after PCI. The periprocedural changes in MR were calculated. The CRP levels at admission were correlated with the pre-PCI MR (r = 0.498, p = 0.001), post-PCI MR (r = 0.429, p = 0.005), and periprocedural changes in MR (r = 0.785, p <0.001). On multivariate regression analysis, the only predictor of the pre-PCI (beta = 0.531, p = 0.002) and post-PCI (beta = 0.471, p = 0.012) MR was the serum CRP concentration. Likewise, the periprocedural changes in MR was predicted by the serum CRP levels (beta = 0.677, p = 0.001) and the presence of angiographic thrombus (beta = -0.275, p = 0.02). In conclusion, these results have shown that the CRP level is related to increased coronary MR in the territory of the culprit lesion. This suggests that inflammatory processes might play a role in microvascular impairment in patients with non-ST-segment elevation acute coronary syndrome. (c) 2013 Elsevier Inc. All rights reserved.