Abstract: Variable gas exchange valves of internal combustion engines include two camshafts, upper and lower, with cams for the combined operation of the valves, so that the upper camshaft acts and contacts a first rocker arm mounted on a fixed shaft and, on its end of greater rocker movement, the first rocker arm has a shaft in pin form which is a mobile shaft of a second, lower, rocker arm of angular form, upon which the lower camshaft cam contacts. The second rocker arm pivoting on the mobile shaft and, because of its angular form, the opposite end to that contacting the lower cam is applied to a valve stem, opening being performed by just one of the cams while closing is the sole consequence of the operation of the other cam, always in combined complementary action.