Atrioventricular junctional ablation （AVJA） combined with biventricular （BiV） pacing is an effective treatment for atrial fibrillation （AF） and rapid ventricular response associated with heart failure. We report the case of a 64-year-old man with dilated cardiomyopathy and AF who underwent AVJA and BiV pacing. Activation imaging is a recently developed novel imaging technique that uses threedimensional speckle tracking echocardiography, which visualizes the left ventricular （LV） intra-ventricular propagation pattern of regional contractions. After AVJA and BiV pacing therapy, interventricular mechanical activation time （IVAT） quantified as the time difference from the QRS onset to regional activation in the 16 segments decreased from 209 ± 92 msec to 177 ± 88 msec. LV free-wall （basal anterior and lateral wall） IVAT values were shorter than those at baseline. Activation imaging appears to be a feasible technique for assessing LV mechanical dyssynchrony.