The function of the left atrial appendage (LAA) reflected by the Doppler flow velocity at the outlet of the left atrial appendage has been reported to be correlated with spontaneous echo contrast and thrombus formation. To evaluate the influence of left ventricular diastole on LAA flow during atrial fibrillation (AF), 81 patients with chronic nonrheumatic AF were studied by transesophageal echocardiography. The peak outflow velocity of LAA during ventricular diastole was higher than that during ventricular systole (0.23 ± 0.14 vs. 0.15 ± 0.13 m/s, p < 0.001). The peak inflow velocity of LAA during ventricular diastole was also higher than that during ventricular systole (0.22 ± 0.15 vs. 0.18 ± 0.11 m/s, p < 0.01). Patients with a good left ventricular ejection fraction have a significantly higher peak LAA outflow velocity and a larger diastolic augmentation of LAA outflow (defined by the difference of LAA outflow between systolic and diastolic phases) than patients with an impaired left ventricular function. Thus, left ventricular diastole might have an influence on LAA flow during AF. In addition, the left ventricular function might be considered a predictor of subsequent thromboembolism from the viewpoint of its effect on LAA flow in patients with nonrheumatic AF.