SQL%notfound

I thought by writing the following it would prevent the user from deleting records if the record exists in a related table but it doesn't work. The coded segment can be found in SQL*Forms v3, KEY-DELREC trigger.

	declare
	  cursor CNV_CUR is
	    SELECT *
	      FROM <table_1> a
	     WHERE a.field = :<block>.<field> ;
	begin
	  if SQL%notfound then
	    delete_record ;
	  else
	    <blah>
	  end if ;
	end ;