BACKGROUND AND OBJECTIVES: Transesophageal echocardiography (TEE) allows a detailed evaluation of the structure and function of the left atrial appendage (LAA) by two-dimensional imaging and Doppler interrogation of appendage flow. LAA dysfunction has been associated with spontaneous echo contrast (SEC), thrombus formation and thromboembolism. The purpose of this study was to define normal heart reference values of LAA maximal forward velocity (LAAV), and to correlate LAAV with cardiac rhythm, mitral valve disease severity, SEC grade and left atrial thrombi development. SUBJECTS AND METHODS: LAA volume measurement and pulse Doppler evaluation of LA appendage flow during TEE were undertaken in 95 subjects; 32 patients with normal heart and 63 patients with various cardiac diseases. RESULTS: Mean LAAV was 87.1+/-26.7 cm/s, mean LAA maximal backward velocity 66.0+/-15.0 cm/s and mean LAA volume 2.2+/-1.2 mL in those patients with normal heart (n=32). There was a negative correlation between LAAV and SEC grade, mitral stenosis severity, LA size and LAA volume. Among those patients with atrial fibrillation, LAAV was lower in the subgroup with LA thrombi than in the subgroup without thrombi (14.9+/-8.1 cm/s (n=16), vs. 29.7+/-21.2 cm/s (n=33), p<0.01). CONCLUSION: Reduced LAAV, SEC and mitral stenosis are all associated with LAA thrombus formation in patients with atrial fibrillation.