  We present a comprehensive study of water drops sliding down chemically
heterogeneous surfaces formed by a periodic pattern of alternating hydrophobic
and hydrophilic stripes. Drops are found to undergo a stick-slip motion whose
average speed is an order of magnitude smaller than that measured on a
homogeneous surface having the same static contact angle. This motion is the
result of the periodic deformations of the drop interface when crossing the
stripes. Numerical simulations confirm this view and are used to elucidate the
principles underlying the experimental observations.
