A cable tensioner includes two cams mounted to face each other that pivot about a common spindle. A torsion spring is centered on the spindle. The torsion spring includes a first end in abutment with a first cam and a second end in abutment with a second cam. The torsion spring applies a torque onto each of the cams to reduce an angular distance between the cams when a cable exhibits insufficient tension. The cable tensioner is placed in a window regulator mechanism to simultaneously tension a lower cable and an upper cable of the device. Furthermore, the tension of one cable through the cable tensioner is reversible since the tension of each cable is balanced with the tension of the other cable.