Background: Different strategies have been investigated for optimizing atrioventricular (AV) synchrony in patients with dual chamber pacemakers (DDD), which has a crucial role in preserving an effective cardiac output. To utilize the Left ventricular 2D speckle tracking strain parameters as a new tool guiding atrioventricular delay (AVD) synchronization in patients with DDD pacemaker to achieve the best LV systolic performance. Method: This interventional cross-over study involved 255 patients with DDD pacemakers, with mean age 50.62 ± 7.03 years, 175 of them were males 68.6% and 80 were females 31.4%. Each device was programmed to 4 different AV intervals, at one-week interval each; (AV pacing /AV sensing):120/100,150/130,180/160, 200/180 msec). Conventional echocardiographic parameters & left ventricular (LV) 2D speckle tracking (ST) strain were interrogated. Results: At relatively prolonged AVD (180/160 msec), both LV longitudinal strain and left ventricular outflow tract velocity time integral (LVOT VTI) were significantly improved (18.11±1.35 & 27.19 ± 3.16 respectively with P <0.001). Also, E/e` showed the lowest values (8.5 ±2.9) and exercise time reached the best between (150/130 and 180/160 msec AVD;309±119 & 320±124, p <0.001 respectively). Conclusions: The benefit of LV speckle tracking based AV optimization looks to result from achieving the best LV systolic performance, this is a very important concern during AV synchronization in DDD pacemakers