The present invention provides imidazoquinazoline derivatives represented by formula (I):
wherein R 1 represents hydrogen, substituted or unsubstituted lower alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted bicycloalkyl, substituted or unsubstituted tricycloalkyl or the like, R 2 represents hydrogen, substituted or unsubstituted lower alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted bicycloalkyl, substituted or unsubstituted tricycloalkyl, substituted or unsubstituted lower alkenyl, substituted or unsubstituted aralkyl or the like, R 3 represents hydrogen, substituted lower alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted bicycloalkyl, substituted or unsubstituted tricycloalkyl, substituted or unsubstituted lower alkenyl, substituted or unsubstituted aralkyl or the like, and R 2 and R 3 are combined to represent a substituted or unsubstituted N-containing heterocyclic group, X represents O or S, or pharmaceutically acceptable salts thereof, which have potent and selective cyclic guanosine 3',5'-monophosphate (cGMP)-specific phosphodiesterase (PDE) inhibitory activity and are useful for treating or ameliorating cardiovascular diseases such as thrombosis, angina pectoris, hypertension, heart failure, arterial sclerosis, as well as asthma, impotence and the like.