Background: Left ventricular (LV) diastolic dysfunction may be a mechanism of left atrial (LA) electroanatomical remodeling in atrial fibrillation (AF). We evaluated the association between LV diastolic function and LA mechanical function in non-valvular paroxysmal AF (PAF). Methods and Results: In 286 patients with PAF (males 73%, 57±11 years), LA size, indexed LA volume, LV diastolic function, and LA appendage flow velocity (LAA-FV) in sinus rhythm were measured using transthoracic echocardiography, transesophageal echocardiography and cardiac computed tomography. The LA voltage map was obtained using NavX contact mapping. Patients with impaired LA mechanical function (LAA-FV <58cm/s, n=142) showed a higher E/Em ratio (10.3 vs. 9.2, P=0.034) and lower Em velocity (6.8 vs. 7.7cm/s, P=0.004) than those with preserved function (LAA-FV ≥58cm/s, n=144). The patient population displayed weak correlations of E/Em with LAA-FV (r=-0.19, P=0.003) and LA voltage (r=-0.23, P=0.004), but more significant association of E/Em and LAA-FV (r=-0.39, P<0.001) for age ≥55 years and LA diameter ≥40mm. E/Em was an independent predictor of LAA mechanical function (β=-0.20, P=0.013) even after age, sex, LA size and comorbidities were controlled for. Conclusions: In patients with non-valvular PAF, LA mechanical function is closely related to the degree of LA remodeling and LV diastolic function. Impaired LV diastolic function significantly contributes to LA electoanatomical remodeling in older patients with a larger LA.  (Circ J 2013; 77: 697–704)