Recent evidence suggests that left atrial (LA) appendage velocities may provide clues to the thrombogenic potential of this structure. Pulsed Doppler evaluation of LA appendage flow during transesophageal echocardiography was performed in 109 patients to evaluate the effects of rhythm, mitral regurgitation, and spontaneous contrast. During sinus rhythm, there was a forward LA appendage contraction wave of 46 +/- 18 cm/sec followed by a retrograde filling wave of 46 +/- 17 cm/sec. In 40% of the patients in sinus rhythm, additional forward and retrograde velocities of 23 +/- 10 and 22 +/- 11 cm/sec, respectively, were seen. In contrast, atrial fibrillation was associated with reduced forward and retrograde flows in an irregularly irregular pattern. In sinus rhythm moderate to severe mitral regurgitation did not appear to affect the LA appendage velocities. Last, although forward LA appendage velocities were found to be significantly reduced in patients with spontaneous contrast by univariate analysis, multivariate analysis demonstrated that only the presence of atrial fibrillation was a significant predictor for spontaneous contrast.