Background: In acute myocardial infarction, indexes of microvascular function measured after percutaneous coronary intervention (PCI) were known to be useful predictors of left ventricular (LV) functional changes and clinical outcomes. We evaluated the usefulness of integrated approach by using index of microvascular resistance (IMR) and coronary wedge pressure (Pcw) in the prediction of LV functional recovery in ST-segment elevation myocardial infarction (STEMI). Methods and Results: Using an intracoronary pressure wire, IMR and Pcw/mean aortic pressure (Pa) were evaluated in 52 patients with first STEMI received primary PCI within 24 hours after onset of symptoms. IMR was defined as distal coronary pressure divided by the inverse of the hyperemic mean transit time. Pcw was measured during inflation of a short compliant balloon placed in the stented segment. Follow-up echocardiography was performed at 6 짹 3 months. IMR and Pcw/Pa had significant correlations with LV regional wall motion score index (WMSI) at follow-up echocardiography (r = 0.464, p=0.001; r = 0.535, p<0.001, respectively). Using receiver-operating characteristics analysis, IMR ��� 33.6 (sensitivity: 74%, specificity: 78%, AUC: 75%), Pcw/Pa ��� 0.28 (sensitivity: 56%, specificity: 83%, AUC: 72%) were the best cutoff values in the prediction for improvement of LV WMSI. In patients with IMR ��� 33.6, Pcw/Pa ��� 0.28, WMSI was improved in 15 patients (94%) of 16 patients, whereas WMSI was improved only in 5 patients (30%) of 17 patients with IMR > 33.6 and Pcw/Pa > 0.28 (p=0.001)(Table). Conclusions: Integrated approach by using IMR and Pcw/Pa was useful in the prediction of LV functional improvement.