Many cardiac rehab facilities use recumbents bikes as well as treadmills during the first 6 weeks post-op. I am a 61 yo physician and had a triple bypass 10 years and 65+ pounds ago and began on a recumbent almost immediately. I would stay on a recumbent or a treadmill for the first 10-12 weeks before trying to ride outdoors. Then I would CAREFULLY begin to bike outdoors again, using a HRM. Obviously, falling would not be good as you could injure your sternum. At 3 months you should be good to go on the bike. I was able to maintain/improve my fitness the 1st three months by daily workouts first at the cardiac rehab and later at the gym. Oh, BTW, you may feel more fatigue than usual until your red blood cell count returns to normal. You should consult your surgeon and/or cardiologist before attempting anything really strenuous. Lastly, as any biker or athlete knows, listen to your body and if something doesn't feel right get it checked out. Best wishes on a speedy recovery.