getting back into exercising

My heel/ankle are really messed up right now and walking hurts, I twisted and then bruised my entire foot, long story. what are some exercises I can do at home (I don't have a pool) that are good cardio? I gained ten pounds since this time last year and I can tell I'm losing muscle. :/ The past three months I've done almost nothing athletic except walk to classes (which is actually quite far but still, just walking) and I really want to start a fitness routine again. Help me figure one out?