For me, the key was the monitoring.
I'm glad I did the rehab, though I was extremely active before the AVR, and at or near the top of the class in fitness during the rehab. I was occasionally bored and/or frustrated, and the solution was monitoring. My rehab clinic administered its own cardiac stress tests -- either bicycling or treadmilling, with a "breathing tube" to monitor CO2 output as well as cardiac monitoring. My initial, relatively wimpy, exercise prescription was based on my on-admission stress test, when I was still on a BB (metoprolol). About a month or two later, I thought I could do lots more, so I requested a repeat test, and got it, with the help of a second rehab nurse (who was filling in for my regular one, one session). Based on that test, they loosened up and raised my exercise prescription significantly.
Soon after that, I also changed my rehab day -- and therefore my class and my rehab nurse -- to suit my personal schedule.
The new rehab nurse was a volleyball player (like me), and also quickly discovered that I love bicycling and don't really love walking or jogging. So she designed a program for me that was like "wind sprints" or "interval training" on one of the stationary bicycles. I'd bicycle gently for 5 minutes, then semi-gently until my HR was in the 120s, then push hard (faster and with more resistance) until I got near my "red line" (143, at 66 yrs old), then back to semi-gently until my HR was back in the 120s, and over and over for 45 minutes, then cool down for 5 minutes. It was a nice tough workout, and I was always dripping sweat when I finished. And my transition back to competitive volleyball -- including 2-on-2 beach -- was uneventful and reasonably easy.
I don't think I would have done as well without the rehab. But I also wouldn't have done as well if I hadn't agitated for some extra monitoring.