AIMS: Thromboxane A2 (TXA2) is a key mediator of platelet activation and aggregation, and an important mediator of platelet-induced coronary artery constriction. We sought to investigate whether baseline plasma levels of TXA2 are associated with coronary no-reflow after primary percutaneous coronary intervention (PPCI). METHODS AND RESULTS: A total of 47 consecutive patients (age, 62.5 +/- 12.7; male sex, 76.6%) admitted to our hospital for a first ST-segment elevation myocardial infarction and undergoing PPCI within 12 h of onset of symptoms were enrolled. Admission TXA2 plasma levels were measured by enzyme-linked immunosorbent assay (ELISA). Angiographic no-reflow was defined as a final TIMI flow of <or=2 or final TIMI flow of 3 with a myocardial blush grade of <2, whereas ST-segment resolution from baseline value of <or=50% was used as ECG index of no-reflow. At multivariable analysis TXA2 plasma levels, endothelin-1 (ET-1) plasma levels, and left anterior descending coronary artery (LAD) as culprit vessel were significant predictors of angiographic no-reflow (P = 0.04), whereas TXA2 and ET-1 plasma levels were the only independent predictors of lack of ST-segment resolution (P = 0.013 and 0.04, respectively). Of note, TXA2 tertiles were independent predictors of both angiographic no-reflow and lack of ST-segment resolution (OR, 3.5; 95% CI, 1.1-11; P = 0.03 and OR, 3; 95% CI, 1.3-7; P = 0.01, respectively). CONCLUSION: TXA2 is an independent indicator of no-reflow that occurs after PPCI. This observation may open new therapeutic opportunity in the setting of PPCI.