Background: Vulnerable plaques have been generally recognized to play a role in the pathogenesis of acute myocardial infarction (AMI), however, the role of circulating CX3CR1+CD163+ M2 monocytes has not been studied properly. We aim to evaluate the features of CX3CR1+CD163+ M2 monocytes and its relationship with cardiac specific markers in AMI patients. Methods: The circulating M2 monocytes were identified in AMI patients (n=35) and healthy controls (HCs, n=10) by flow cytometry using two staining methods: CD68+CD163+ (cytoplasmic staining) and CX3CR1+CD163+ (surface staining). CX3CR1+ monocytes were purified by magnetic cell sorting. The expression level of peroxisome proliferator-activated receptor γ (PPARγ) and arginase-1 (Arg-1) were measured by real-time quantitative PCR and Western Blot in CX3CR1+ monocytes. Results: Circulating M2 monocytes extremely expanded in AMI patients compared with HCs (P<0.01). Positive linear correlation was confirmed between CD68+CD163+ and CX3CR1+CD163+ cell populations in AMI patients (r=0.39, P=0.02). The percentage of circulating CX3CR1+CD163+ M2 monocytes positively correlated with cardiac specific markers (cTNT, CK-MB) and acute phase markers (glucose, hs-CRP) (cTNT, r=0.63, P<0.01, CK-MB, r=0.54, P<0.01, glucose, r=0.62, P<0.01, hs-CRP, r=0.58, P<0.01). CX3CR1+ monocytes in AMI patients expressed higher levels of PPARγ and Arg-1 than those in HCs (P<0.01). Conclusions: Circulating M2 monocytes increased in AMI patients and positively correlated with the elevation of both cardiac specific and acute phase markers. CX3CR1+CD163+ M2 monocytes might have application value for the early diagnosis of AMI.Keywords: Acute myocardial infarction (AMI); M2 monocytes; cardiac markers.