Abstract: Objective To investigate the expression of connexin 43 (Cx43) in peripheral blood monocytes (PBMCs) from patients with acute coronary syndrome (ACS) and its clinical implications. Methods We prospectively collected the clinical data from 40 patients with ACS including 20 with unstable angina pectoris (UAP) and 20 with acute myocardial infarction (AMI) admitted in our department between January, 2018 and June, 2018, with 20 healthy subjects undergoing routine physical examinations serving as the control group. Peripheral blood samples were obtained from all the participants and plasma and PBMCs were separated. Enzyme-linked immunosorbent assay (ELISA) and turbidimetric inhibition immunoassay (TIIA) were used for analysis of plasma levels of interleukin (IL)-1β and high sensitive C-reactive protein (hs-CRP), respectively; real-time quantitative RT-PCR and Western blotting were used to detect the mRNA and protein levels of Cx43 in the PBMCs. Results Compared with the control group, the patients with UAP showed significantly increased plasma levels of IL-1β and hs-CRP (P< 0.001) and obviously elevated expressions of Cx43 at both mRNA and protein levels in the PBMCs (P<0.001). Compared with the patients with UAP, the patients with AMI had significantly higher plasma IL-1β and hs-CRP levels (P<0.001 and P<0.01) but lower expression levels of Cx43 in the PBMCs (P<0.05). Conclusion Patients with UAP and AMI have activated inflammatory responses and reverse changes in Cx43 expression in the PBMCs, suggesting the different roles of Cx43 in the pathogenic mechanisms of different types of ACS.