Lili, you have to listen to your surgeon on this. He or she will let you know when it's appropriate to start exercising. DO NOT push this - you have to heal fully. I had a reconstruction and found that Pilates and the less aggressive forms of yoga were very helpful. As for burning calories, the treadmill and elliptical machines, or stationary bike, are all good. If you can afford it, your local fitness center might have a trainer who could give you a few private sessions, geared to the surgery you've had. You just don't want to do anything too soon that stretches your chest too far, so, as I said, please check with the surgeon before starting anything.  Good luck - PJH