Background: It is unknown if CHADS2 score, a marker of chronic thromboembolic risk in atrial fibrillation (AF), predicts left atrial (LA) appendage and left atrial function on transesophageal echocardiography (TEE). Methods: We retrospectively studied patients undergoing TEE for nonvalvular AF at our hospital from June 2008 June to June 2010. CHADS2 score was derived by assigning 1 point for congestive heart failure (CHF), hypertension, age 75, and diabetes and 2 points for stroke or transient ischemic attack. Spontaneous echo contrast was defined as dynamic smoke-like echoes within the atrial cavity with the characteristic swirling motion that could not be eliminated by changes in the gain settings. Peak LAA ejection and filling velocities and peak RAA ejection and filling velocities were measured by placing a pulsed wave Doppler sample volume just inside the base of the appendage. The association between CHADS2 and LAA appendage velocity was evaluated. Results: In 418 consecutive patients undergoing TEE, 158 patients were enrolled for this study. SEC was seen in 67 patients. LA size and volume was significantly larger among patients with SEC group than non-SEC group ( p=0.022, p=0.004 ). Peak LAA ejection and filling velocities were significantly lower in patients with SEC group than non-SEC group ( p=0.009, p=0.001 ). A strong association was present between the CHADS2 score and Peak LAA ejection and filling velocities (p = 0.001, p=0.003 ). Conclusion: In AF, CHADS2 is strongly associated with LA appendage function and SEC on TEE. Our findings support that CHADS2 score is useful way to evaluate the anatomical and functional capacity of LA and LAA.