The etiology of dilated cardiomyopathy associated with congenital complete AV block has not yet been clarified. Two infants with AV block of autoimmune and surgical etiology, respectively, had received a dual-chamber right ventricular-based pacemaker and developed dilated cardiomyopathy with severe septal to left ventricular free-wall dyssynchrony 3.4 (0.9) years later. After 4 weeks of biventricular pacing and spontaneous junctional narrow QRS rhythm, respectively, both children showed significant improvement in left ventricular function along with reverse remodeling. Thus, electromechanical dyssynchrony associated with conventional right-ventricular-based DDD pacing may play a significant role in the development of dilated cardiomyopathy in the young.