Sicilian Defense: Heidenfeld Variation

The Sicilian Defense: Heidenfeld Variation is a chess opening classified under ECO code B22 in the Semi-Open Games family, where Black responds to 1.e4 with something other than 1...e5, including the Sicilian Defense, Caro-Kann, and Pirc. It is reached after 5 moves: 1. e4 c5 2. c3 Nf6 3. e5 Nd5 4. Nf3 Nc6 5. Na3. The resulting position leaves black to move.