Compounds of formula Ia or Ib:wherein A, W, X, Y, R1, R2, R3 and R4 are as defined herein. According to the invention, this novel galenical form contains a therapeutically effective amount of molsidomine or one of its active metabolites and has an in vitro dissolution rate measured spectrophotometrically at 286 or 311 nm by the method described in the European Pharmacopoeia, 3rd edition, at 50 rpm, in 500 ml of a 0. The present invention solves the problem that there is a lack of the MSRP transmission link in the large message mode in the prior art.