  We present preliminary results of 3-D hydro simulations of the interstellar
medium evolution in dwarf spheroidal galaxies undergoing star formation for the
first time. The star formation is assumed to occur in a sequence of
instantaneus bursts separated by quiescent periods. Different models are made
changing the number and the intensity of the bursts in such a way that the
final mass of the formed stars remains the same. We followed the enrichment of
the ISM taking into account the contribution of both type Ia and II supernovae.
The aim of our models is to find a star formation history compatible with the
observed spread of stellar age and metallicity in such galaxies and to
reproduce the observed mass-metallicity relation.
