Background:In AMI, it was not clearly defined whether the coronary wedge pressure of infarct-related artery is related to the degree of microvascular damage or degree of collateral circulation. We evaluated the relationship between the Pcw/Pa (coronary wedge pressure / mean aortic pressure) and microvascular integrity in AMI patients following primary PCI according to presence, or not presence of angiographic collateral circulation. Methods: The study population was consisted of 33 patients (57짹12 years old) with first AMI. After primary PCI, we evaluated the TIMI grade, TIMI myocardial perfusion grade (TMP grade) and the coronary flow reserve (CFR), hyperemic microvascular resistance index (hMVRI), and Pcw/Pa by intra-coronary Doppler and pressure wire. The study patients were divided into two groups; group 1 (n=23): Rentrop collateral grade=0, group 2 (n=10): Rentrop collateral grade���1. We performed FDG-PET at 7 days after PCI. Results: After PCI, the Pcw/Pa was significantly correlated with the TMP grade, hMVRI, CFR, DDT (diastolic deceleration time) and FDG uptake rate in group 1. However, the Pcw/Pa was not correlated with the TMP grade, hMVRI, CFR, DDT and FDG uptake rate in group 2 (Table). Best cutoff value of the Pcw/Pa for 50% of FDG uptake was 0.33 (AUC=0.667, sensitivity 42.1%, specificity 92.9%). Conclusion: The post-PCI Pcw/Pa in AMI may be an useful indicator of the severity of microvascular damage of infarct-related myocardium in patients without developed collateral circulation, but it can not represent the severity of microvascular damage in patients with already sufficiently developed collateral circulation.