I'll just add to the chorus here. Yes, they take it very slow at first, but you can get them to change the exercise level after a week or two once they are confident you're ready for it. Most of their clientele have serious underlying heart damage (post-MI or bypass) that makes exercise much riskier than us valve replacement types. Still, I think they are doing the right thing. Also, once they accelerate your exercise level, expect them to still be concerned at times when they see your heart rate at 160, again because that would be a serious red flag in most of their clientele.
Sure, you could do rehab or your own, but will you? I found the regular schedule of my rehab sessions, the charted progress, the heart rate and BP monitoring, the periodic counselling of the staff, and the review and exercise plan they gave me after I completed the 12 Week phase "phase 1" program to be very, very helpful and probably the most important thing in the success of my recovery.