To provide compounds which are useful as the cGMP PDE5 inhibitor.

The compounds represented by formula 1A and formula 1B (wherein R1, R2, R3, Het1 and X are each as defined in the specification) which are useful for treating and preventing medical conditions in which cyclic guanosine-3',5'-monophosphate phosphodiesterase is expected to be inhibited are provided. The compounds of the present invention are useful for treating and preventing the medical conditions in which cGMP PDE5 is expected to be inhibited (male ectile dysfunction (MED)), impotency, female sexual function dysfunction (FSD), clitoris dysfunction, female low-active sexual craving dysfunction, female sexual wakefulness disorder, female sexual pain disorder, female sexual feeling dysfunction (FSOD) and so on).