If you can't do a bike then try the following,
Use an arm ergometer it's an excellent substitute for bicycling. The arm ergometer is a machine that allows you to use your arms in place of your legs to push the pedals of a bicycle. Another option is trying an upper body circuit training program, using high repetitions and low loads, and short rest breaks between exercises. Using upper body machines or free weight exercises that work your latissimus dorsi, deltoids, pectorals, biceps, triceps and rhomboids will get your heart pumping.