Abstract: A gear shifting mechanism intended to be integrated into an horological movement includes a gear pinion rotated by a first wheel of the movement, an element holding a first fly-back heart freely mounted on the gear pinion, and rotated by the first wheel or by a second wheel of the movement. A second fly-back heart is attached to the gear pinion, a gear wheel is mounted freely rotating around the gear pinion and holds a first hammer or also a second hammer pretensioned against the first heart or also the second heart by a first pretensioning spring or also a second pretensioning spring, and a shift wheel being rotatably mounted on the periphery of the gear wheel (4.6) holds a first cam or also a second cam.