Background: Coronary wedge pressure (PCW) is known to be an useful index of microvascular integrity in acute myocardial infarction (AMI). During measurement of PCW, microvascular resistance of infarct-related myocardium may affect the PCW wave patterns. We evaluated the relationship between PCW wave patterns and microvascular resistance and left ventricular (LV) functional recovery. Methods and Results: Using an intracoronary pressure wire, PCW and index of microvascular resistance (IMR) were evaluated in 52 patients with first STEMI received primary PCI within 24 hours after onset of symptoms. PCW was measured during inflation of a short compliant balloon placed in the stented segment. IMR was defined as distal coronary pressure divided by the inverse of the hyperemic mean transit time. Systolic pressure (PCWsp), pulse pressure (PCWpp) of PCW and PCW were well correlated with IMR (r = 0.500, p < 0.001; r = 0.467, p < 0.001; r = 0.382, p = 0.005, respectively), whereas diastolic pressure (PCWdp) of PCW had a weak correlation with IMR (r = 0.273, p = 0.050). PCWsp was also correlated with LV wall motion score index (WMSI) and ejection fraction (EF) at admission (r = 0.379, p=0.006; r = -0.393, p = 0.004, respectively) and follow-up (r = 0.455, p = 0.001; r = -0.426, p = 0.002, respectively) measured by echocardiography. Using receiver-operating characteristics analysis, PCWsp ��� 45 mmHg was the best cutoff value in prediction of LV functional improvement (sensitivity: 59%, specificity: 83%, accuracy: 70%). In patients with PCWsp ��� 45 mmHg, baseline and follow-up WMSI were significantly lower than those in patients with PCWsp > 45 mmHg (1.47 vs.1.64, p=0.013; 1.25 vs. 1.47, p=0.009). In patients with PCWsp ��� 45 mmHg, WMSI was improved in 20 patients (83%) of 24 patients, whereas WMSI was improved in 14 patients (50%) of 28 patients with PCWsp > 45 mmHg (p=0.019). Conclusion: PCWsp is an useful index for evaluation of the degree of microvascular damage and correlated with LV functional recovery in AMI patients.