What sort of cardio is safe for a heel injury? besides a pool, is the stationary bike ok?

Yes: Cycling is good. I would try to keep the pressure on the ball of the foot in the pedal area. A rowing machine would be another option. The airdyne bike also has upper body resistance levers, handles and the feet can actually rest.

Yes, usually: Depends on the type of injury.I recommend non weight bearing activities such as: swimming, cycling, rowing and lifting weights(sitting or lying position only).Use a floatation device in swimming to keep weight off. Stay in the saddle with cycling. Sometimes these can aggravate the foot, start slowly. Many times you don't know you are overdoing until you have already overdone it. Be careful. Dr l.