  The isochronicity problem is a classical problem in the qualitative theory of
planar vector fields which consists in characterizing whether a center is
isochronous or not, that is, if all the trajectories in a neighbourhood of the
center have the same period. This problem is usually investigated by means of
the so-called period function. In this paper, we are interested in exploring
the isochronicity problem for tangential centers of planar Filippov vector
fields. By computing the period function for planar Filippov vector fields
around tangential centers, we show that such centers are never isochronous.
