CREATE TABLE table_name_7 (opponent VARCHAR, game_site VARCHAR, record VARCHAR)

Which Opponent has a Game site of heinz field, and a Record of 3 1?
SELECT opponent FROM table_name_7 WHERE game_site = "heinz field" AND record = "3–1"
SELECT "opponent" FROM "table_name_7" WHERE "3–1" = "record" AND "game_site" = "heinz field"