Strain rate (SR) imaging enables quantitative measurement of left ventricular (LV) function independent of cardiac translation. However, whether SR imaging is applicable for detection of left atrial (LA) dysfunction remains unknown. The purpose of this study was to assess the feasibility of measuring LA function by SR imaging, focusing on the effects of aging and LA dilatation during atrial fibrillation (AF). Echocardiographic evaluation including SR imaging was performed in 50 controls (29 males and 21 females; mean age, 41 +/- 14 years) and in 27 patients with AF (15 males and 12 females; mean age, 62 +/- 12 years; 8 with persistent AF and 19 with paroxysmal AF) from 3 apical views and analyzed off-line. Peak SR was measured at each LA segment (septum, lateral, posterior, anterior, and inferior), and mean peak systolic SR (SR-LAs), early diastolic SR (SR-LAe), and late diastolic SR (SR-LAa) were calculated by averaging the results for each segment. LA dimension, peak mitral and pulmonary velocities at late diastole, LA fractional shortening, and atrial filling fraction were calculated as parameters of LA function. Normal values for mean SR-LAs, SR-LAe, and SR-LAa were 3.4 +/- 1.0 s -1 , -3.9 +/- 1.7 s -1 , and -3.1 +/- 1.0 s -1 , respectively, and they were successfully measured in more than 95% of the LA segments. In controls, both mean SR-LAs and mean SR-LAe correlated with age, LA dimension, and early to late diastolic mitral flow velocity ratio. Conversely, mean SR-LAa did not show significant correlation with age or parameters of LA function. In AF patients, mean SR-LAs was correlated inversely with age. The mean SR-LAs was significantly lower in persistent AF patients than in age-matched controls (1.7 +/- 0.8 vs 2.9 +/- 0.9 s -1 ; P < .01). Based on our findings, we conclude that noninvasive quantification of LA function using SR imaging enables evaluation of LA dysfunction due to aging and LA dilatation.