Need alternative for me current cardio work out.

I used to run a bit, not much. Maybe about a mile or two a day. But I have recently noticed a problem with my foot and I was told running is not an option anymore. The navicular bone in both of my feet grew in as two bones, instead of one (it is normally a single bone in the inside of your foot). This causes the cartilage between the two bones to get very very irritated when too much stress is put on it, and cause fluid to build up. Basically it feels like my arches are going to collapse and a bone is going to pop out of the inside of my feet. So I like to try and avoid that feeling. Running and intense Spin classes are the only things that really irritate it, but those are the two things that I feel give me the best workout. I also don't notice near the same results from the elliptical as I do from running or spinning in the past.

Any suggestions on what cardio oriented exercise I could incorporate so that my foot doesn't get inflamed, but I am still getting a vigorous workout? Stair master is currently at the top of my list, I just want other input!

**EDIT: Fuck me and my inability to proof read. It should be MY cardio workout in the title.