human
Considering the provided database schema and associated query, produce SQL code to retrieve the answer to the query. 
###Database Schema: Week, Date, Kickoff (ET), Opponent, Result, Record, Game site, NFL Recap
###Question: Which Opponent has a Game site of heinz field, and a Record of 3–1?
gpt
SELECT Opponent FROM table WHERE Game site = heinz field AND Record = 3–1