In atrial fibrillation (AF), the reasons why most of the thrombi form in the left atrium are mainly unknown. In the vasculature, endothelial damage together with platelet activation and inflammation contribute to initiation of blood coagulation and thrombus growth. The purpose of this study was to investigate whether atrial-specific differences in endothelial damage, leukocyte activation, platelet stimulation occur in patients with AF. Twenty patients (15 men, 5 women; age 55 ± 8 years, 15 paroxystic AF, 5 persistent AF) with AF undergoing ablation were investigated. Blood samples from the left and right atrium were obtained at the start of the procedure. Procoagulant microparticles (MPs), reliable markers of vascular damage were measured by capture assays. Their procoagulant abilities were quantified by functional prothrombinase assay and their cellular origin were determined (endothelium, platelet, leukocyte). In addition, platelet reactivity was evaluated by whole blood flow cytometry for expression of platelet Pselectin (CD62P), active glycoprotein IIbIIIa receptor (PAC-1). Platelet aggregation was evaluated using Arachidonic acid (AA), ADP, TRAP and collageninduced whole blood aggregometry. No atrial-specific differences in the levels of total procoagulant MP, leukocyte-derived-MP and platelet-derived MP could be evidenced. Conversely, endothelial-derived MPs (CD105+) were slightly elevated in the right atrium (RA 0.96 ± 0.53 vs. LA 0.80 ± 0.45 nm PhtdSer Eq.; p = 0.041). Likewise, collagen-induced platelet aggregation was evidenced in the right atrium (Collagen 1 mg/l RA: 48 ± 33% vs LA 37 ± 29%; p 0.035; collagen 2,5 mg/l RA: 76 ± 25% vs LA: 60 ± 29%; p = 0.001). In patients with AF, endothelial damage and collageninduced platelet aggregation appear slightly more pronounced in the right atrium. Our data did not substantiate the view that chamber specific enhanced thrombogenic status could be a reliable explanation for the increased propensity for thrombus formation observed in the left atrium in AF patients.