Objective: This study demonstrated left atrial endocardial dysfunction and platelet activation in patients with atrial fibrillation and mitral stenosis. Methods: Study included 80 patients with mitral stenosis and atrial fibrillation (40 each with and without left atrial thrombosis), 15 healthy volunteers, and 10 left atrial appendage (LAA) specimens from donor hearts. Blood samples were collected through peripheral vein and left atrium, with peripheral blood samples of volunteers as controls. LAA specimens were collected during operations. LAA expressions of von Willebrand factor (vWF) and P-selectin were determined immunohistochemically; plasma concentrations were measured by enzyme-linked immunosorbent assay. LAA expressions of vWF and P-selectin genes in were quantitated with real-time fluorescent quantitative polymerase chain reaction. Results: The difference in vWF and P-selectin plasma levels between left atrial and peripheral venous blood was not significant; however, peripheral plasma levels of vWF and P-selectin were significantly higher in those with thrombosis than without thrombosis, which in turn were higher than in healthy subjects. Both vWF and P-selectin proteins were stained in both left atrial endocardium and cardiomyocytes. The normalized vWF gene expression relative to control was 3.04 in patients with thrombosis and 2.16 in those without thrombosis (P < .01). The difference in P-selectin gene expressions among the groups was not significant. Conclusions: No differences were observed in plasma levels of vWF and P-selectin between left atrial and peripheral venous blood. Over expression of vWF gene in LAA may contribute to increased plasma vWF levels. P-selectin and vWF together may play a role in thrombosis.