Inflammation and oxidative stress play an important role in destabilizing artherosclerotic plaque in patients with acute coronary syndrome. In the present study we tried to establish the role of myeloperoxidase, an inflammatory marker secretory of activated neutrophils, in the diagnosis and prognosis of patients with acute chest pain presenting to the emergency department. In our study, MPO (myeloperoxidase) was determined at three different times: T1 – at the admission; T2 – at 48 hours from the admission; T3 – at discharge. MPO can be a diagnostic marker for patients with NSTEACS because it has significantly higher values compared to the control group, from the moment of their presentation in the emergency department (1.7364±0.8356 U/ml, pT<0.0001), even in patients with normal troponin levels. Also, MPO can be considered as a prognostic factor of patients with acute coronary syndrome, presenting significantly increased values in patients with unfavorable evolution compared to those with favorable evolution, throughout the hospitalization (T1 – 2.400 U/ml versus 1.4641 U/ml, pT = 0.0002; T2 – 2.6625 U/ml versus 1.8333 U/ml, pT = 0.0102; T3 – 2.6813 U/ml versus 1.500 U/ml, pT = 0.0006).