The invention relates to bicyclic heterocyclic compounds of general formula ##STR1## wherein A to F, Y.sub.1 and Y.sub.2 are defined as in claim 1, the tautomers thereof, the stereoisomers thereof including their mixtures, and salts thereof, particularly the physiologically acceptable salts thereof with organic or inorganic acids or bases, which have valuable pharmacological properties, preferably aggregation-inhibiting effects, pharmaceutical compositions containing the compounds and processes for preparing them as well as new intermediate products of general formula Ia.