An aromatic nitrogen-containing 6-membered cyclic compound of the formula (I): <；CHEM>； wherein Ring A is a substituted or unsubstituted nitrogen-containing heterocyclic group； R<；1>； is a substituted or unsubstituted lower alkyl group, -NH-Q-R<；3>； (R<；3>； is a substituted or unsubstituted nitrogen containing heterocyclic group, and Q is a lower alkylene group or a single bond), or -NH-R<；4>； (R<；4>； is a substituted or unsubstituted cycloalkyl group)； R<；2>； is a substituted or unsubstituted aryl group； one of Y and Z is =CH-, and the other is =N-, or a pharmaceutically acceptable salt thereof, these compounds exhibiting excellent selective PDE V inhibitory activities, and hence, being useful in the prophylaxis or treatment of penile erectile dysfunction, etc.
