Cardiac rehab lasts 12 weeks--three hours per week. I am already a member of a gym and have been going regularly but I simply do not push myself the way the nurses and trainers push us at rehab. The exercises started out easy and are getting harder and harder. I know I won't be pushing myself in my own gym after rehab is through. I just won't because sometimes I just want to stop the rehab and sit down for a while (but they won't let you.) Will I be losing what I gained at rehab and not be helping my heart if I just exercise at the pace I normally exercise? At my own gym I plan to exercise on each piece of equipment at whatever pace I ended up with at the rehab gym if I possibly can or possibly less because it is getting harder and harder at rehab. We don't have one or two pieces of equipment at my gym that are available at rehab but there are plenty of others.
If you continue to work out at the same intensity, duration, and frequency as you are at rehab, you will maintain the fitness level which you have reached. You say however that you want to exercise less than they are pushing you at rehab, which means you will probably see an commensurate drop in fitness. This is not inherently a bad thing, it just depends on your goals.