Since LV pacing is currently delivered on the epicardium by a lead inserted in coronary sinus (CS) branches, the interface between the point of pacing delivery on LV surface and the underlying LV wall, and overall lead movements inside coronary sinus might describe some underlying myocardial mechanics. By means of a recently published fluoroscopy-based method, the trajectory of the electrode tip inserted in CS branches can be reconstructed in three-dimensions (3D) throughout the cardiac cycle. A preliminary clinical pilot study (Heart Rhythm 2013;10:1360) demonstrated that biventricular pacing acutely induced changes in trajectory geometry, which were correlated to the echocardiographic volumetric response to CRT at six-month post-implant follow-up. In responders only, biventricular pace abruptly determined a more circular shape. Such results were "hypothesis-generating" and are to be yet tested on a larger scale.