Left atrial (LA) dilatation is a powerful predictor of cardiovascular morbidity and mortality. LA longitudinal strain parameters evaluating reservoir, conduit and contractile strain can represent LA functions. We investigated the association between LA strain and left ventricular (LV) functions using speckle-tracking echocardiography in children with mitral regurgitation in 45 asymptomatic mitral regurgitation patients graded as mild, moderate and severe. LV strain was lower in the moderate group (–17.8±3.7%) and further reduced in the severe regurgitation group (-16±2.14%) in comparison with the reference group (-20.5±6.2%). Regarding LA functions, reservoir strain was higher in the severe and moderate mitral regurgitation groups (38±12.9% and 40.7±9.5%, respectively) in comparison with the controls (40.0±7.2%; p<0.0001). A milder depression of contraction was observed in the severe group (12.2%) than in the moderate group (13±7.2%). In the moderate and severe groups, LV strain correlated significantly with the vena contracta (r=–0.858; p=0.04). Vena contracta was the only independent association for LV longitudinal strain. ROC curve analysis predicted LV longitudinal strain as shown by vena contracta, with a cut-off value >5.65 mm. Vena contracta had a positive predictive value of 75% for predicting LV function. We propose the use of LA and ventricular strain during the follow-up of asymptomatic children with mitral regurgitation. Also, a vena contracta diameter of >5.6 mm can be used as a threshold for LV function impairment.