In the current study, we evaluated the dynamics of oxidative stress markers in patients with acute myocardial infarction (AMI) treated by primary percutaneous coronary intervention (PCI). Thirty consecutive patients with AMI with ST elevation were included. Plasma lipid peroxidation end product malondialdehyde (MDA) and total antioxidant capacity (TAC) in blood plasma were evaluated. Peripheral venous blood samples were obtained prior to reperfusion and at five time points after reperfusion. The control group consisted of 20 ischemic patients without acute coronary syndrome. TAC in the AMI group at admission was lower than in control patients (1.26 + 0.32 vs. 1.52 + 0.24 mmol/l). Within 1 h after reperfusion, in most cases, values significantly declined (1 min, 1.10 + 0.33 mmol/l; 1 h, 1.06 + 0.21 mmol/l [p= 0.03]). After 3 h, values began to increase (1.14 + 0.29 mmol/l) and returned to basal values after 3 d (1.29 + 0.24 mmol/l). MDA levels in AMI patients at admission were higher than in control patients (1.66 + 0.55 vs. 1.44 + 0.55 mmol/l) but showed a sustained decrease over the 3 h after reperfusion of the occluded artery (1 min, 1.57 + 0.37 mmol/l; 1 h, 1.50 + 0.35 μmol/l; 3 h, 1.35 + 0.59 μmol/l [p = 0.03]). Reperfusion of the occluded coronary artery by PCI in AMI lead to an immediate decrease in TAC, suggesting formation of reactive oxygen species. However, the MDA level significantly decreased after reperfusion. This may suggests less reperfusion injury after PCI.