how do I do to get the foreign keys of a table?

This is my SQL to return the constraints...

select tgconstrname, tr.relname, fr.relname from pg_trigger, pg_class tr,
pg_class fr
where tr.oid = tgrelid and fr.oid = tgconstrrelid and
tr.relname='MyTableName'

 so, how do I do to get the  foreign keys of a table?

let me be more explicite, I want to get the name of fields from a table that
are related with other table! (foreign key)

NOTE: I want a SQL command to get it from any table of any PostgreSQL
database, so it can not be a function!

please help me

tia

Roberto de Amorim