Here is sound advice from a two time bypasser. First was 31 years ago, second was almost 4 years. Had aortic valve replaced with St. Jude's. The shortness of breathe is normal after bypass, the lungs are healing and must get build back up. It takes time, walking everyday a little. You should have had exericises that was done to help clear the lungs. Now the walking would help build the lungs back to health. You should not push doing anything right away. Talk with your cardio about anything you should be doing while you are healing. There is cardio rehab that can help, if insurance covers well. Otherwise, just take short walks and build that up gradually. Best exercise there is. And keeps one toned as well. Good luck and do not rush the healing, it takes time. And the shortness of breathe will pass in due time. Hang in there.