Background and Objectives: Fibrinogen induced erythrocyte aggregation. Increased plasma fibrinogen concentration have been associated with an increased risk of cardiovascular events, while left atrial spontaneous echo contrast (LASEC) has been associated with thromboembolic strokes. We evaluated relation between LASEC and the constituents of the blood and plasma fibrinogen concentration in patients with AF. Methods: Forty-nine patients (mean 65 years old, 29 men) underwent transthoracic echocardiography (TTE) and transeophageal echocardiography (TEE). The presence of LASEC by TEE were determined independently by two different echocardiologists. Complete blood count, mean platelet component (MPC), fibrinogen, Hs-CRP, and homocystein concnetrations were measured. Results: LASEC was present in 39 patients and more increased plasma fibrinogen concentration was measured than patient without LASEC (3.6짹0.7 g/L vs. 2.9짹0.5 g/L, P=0.034). No difference was in MPC concentration, Hs-CRP level, and platelet count according to presence of LASEC. Increased LA size and decreased LAA velocity in patients with LASEC compare to patients without LASEC. (Table) Conclusion: LASEC is associated with increased plasma fibrinogen concentration, enlarged LA , and depressed LAA function.