This is NOT how you "defeat" the Petrov, and 4.Nxf7 is hardly "amazing". The Cochrane Gambit is a speculative sac that should lead to no real danger for black against correct play. Plus, after 5.Bc4+ black should reply with the freeing move 5...d5. After the main continuation 6.Bb3 Be6 7.e5 Ne4 8.d4 c5 9.Qf3+ Ke8, black has a very good game.
This opening is playable if white is well prepared and especially if it is a blitz game, but one thing is for sure: the Cochrane Gambit is not the best way to play against the Petrov and certainly does not "defeat" the Petrov with some sort of "amazing attack". Be careful with your wording.
Check out this cool attack against the Petroff Defense!
Material is about even (in most games where I have two pawns for a knight I win) and white's position is clearly better.
Here's what happens if black isn't so careful.
EDIT: Feel free to post advice and/or constructive criticism.