I'm not an expert on pacemakers (yet), but I think it is important that you tell your pacemaker doc about the lifestyle you led before surgery and how you plan to live after. Tell them about your physical activities, intensity, plans, travel plans - be sure they know what demands you want to place on the pacemaker. They should then be able to tell you the specific adjustments that they can do with your device. All of them have ways to adjust minimum and maximum paced heart rate. (If your natural pacing sometimes works, and if it goes higher than your pacer goes, the pacer lets natural pacing take over.) Most also have "rate responsive" features that can sense when extra demand is placed on your heart and increase your heart rate accordingly. In the early stages of recovery from valve surgery they may want to set things low to allow healing to take place. This is OK as long as they will readjust things once your heart has healed more. Also, if you are going to do cardiac rehab, the rehab tech's can often see when adjustments are needed to your pacer. The tech's monitor your heart rate and rhythm as you work, and they can tell if your pacemaker is holding you back. As an example, when I was in rehab, I was able to work on a treadmill just fine. The bouncing of walking caused my pacer to increase my heart rate, allowing me to exercise to my allowable limits. Once I moved over to a stationary bicycle, though, the exercise no longer caused me to bounce up and down as I rode, so my heart rate did not go up. The tech's recommended to my pacer doc that he turn on "rate response" so that the pacer would sense when my breathing rate increased, and increase my heart rate then, too. It made a world of difference, but it never would have come up if I had just accepted the default settings when my pacer was implanted. (I think they set them all as if you are a chari-bound 80-year-old at first, just to see what you really need.)
The other thing to keep in mind is that getting to the proper settings for your individual needs is not a one-visit event. It will take some time and some trial and error to get what you want, but it is worth the effort. I am 2 years into the process and I'm not finished yet. I am, however, much happier with it now than I was earlier in the process.