Oxygen in transfer

Okay so I had a little mishap in transferring into my secondary. I have a

6.5% stout that I transferred, but in the middle of transfering I ran into a pressure problem. The problem wa basically that I did not notice that there was no air passage into the primary. So when all of the air was "sucked" out of the primary it looked for more air and decided that sucking that air through the racking cane from the secondary and back into the primary was a good idea. Needless to say it sucked back enough air to cause an eruption of air bubbles in the primary fermenter. What effect does the oxygen have on the beer at that point? What off flavors (if not contaminated) is this likely to produce? Thanks in advance.