Introduction: Coronary artery disease (CAD) is associated with higher platelet activation sometimes despite aspirin use. There are conflicting data concerning platelet activation course during physical exercise in patients on aspirin with CAD. Aim: To assess platelet activation pattern during physical exercise in patients with CAD. Methods: The study included 35 patients (20 men, 15 women) aged 64.7±10 years with CAD (CCS II) on aspirin treatment (75 mg daily) and a control group of 10 healthy subjects adjusted for age and gender. Treadmill testing was performed using the Bruce protocol. Platelet aggregation was measured with optical aggregation with the agonists ADP (10 µM), collagen (2 µg/ml) and arachidonic acid (0.5 mg/ml) before and at peak exercise; P-selectin platelet and soluble expression (basal and after stimulation with thrombin) was assessed with cytofluorometry before, at peak exercise and 1 hour after. Results: There were no differences in collagen and ADP aggregation between patients and the control group. There was a significant increase of ADP aggregation at peak exercise in the control group (p <0.05). There was a positive correlation between platelet aggregation before exercise and at peak exercise with ADP (r=+0.86) and with collagen (r=+0.61). There was no difference in soluble P-selectin concentration between patients and the control group. Platelet P-selectin expression without stimulation with thrombin 1 hour after exercise was significantly higher in patients than in the control group (p <0.05). Conclusions: 1. Physical exercise does not intensify platelet aggregation in patients with CAD on 75 mg aspirin daily. 2. Despite taking aspirin, platelet activation measured with the expression of platelet P-selectin increases and there is further intensification during exercise testing. 3. The concentration of soluble P-selectin in patients with CAD does not reflect the expression of platelet P-selectin.