I had a bicuspid aortic valve and had to have it replaced by open heart in May 2018 (cow valve). I was pretty active before that, racing outrigger canoes, biking, hiking, and lifting at the gym. Reading up about post-surgery exercise after the surgery, people would say that they could go back to playing golf after 3 months. I hate golf. Three months after my surgery I was back paddling a one-man outrigger canoe and coaching 6-man, but not racing. I was hiking (3-4 miles) and biking (10-12 miles.) I paddled throughout the winter season. I coached novice in 2019 and raced 6 Iron races (10-12 miles) in a 6-man, medaling 5 times. Pandemic halted coaching and racing in March 2020, but I coached 5 months in 2021 and did long racing pieces in the ocean, although there were only 3 sanctioned races all season and I did not race. I coached this year and raced Iron races in rocking water in the ocean. Last week and last night's practices were in pretty heavy seas for off the coast of SoCal and I steered a boat with only 4 paddlers and we rocked it. I just turned 73. What I don't do is heavy lifting, and since the pandemic I have not been back to the gym (petri dish, you know.) I have TRX straps and do 15-20 minutes of body weight and stretching exercises every morning. I do light kettlebell exercises (10 and 20 lbs.) 3 times a week or so. I gained 5 lbs. of weight after doctors put me on blood thinners (Xeralto) which I can't seem to get off no matter the diet and exercise. (I had ablation in December, developing A-fib and A-flutter after the open heart surgery.)
In short, there is a lot of exercise you can do to stay fit and active. You may not be able to lift heavy weight anymore because of the pressure on the heart (don't know if I should do it at my age, anyway), but you can stay very active and keep fit. Also, I strongly recommend going through cardiac rehab. It made a huge difference for me. I went to cardiac rehab starting 6 weeks after surgery and kept at it for 8 weeks until they felt I was stable, healed, and getting fit. I have a fellow paddler that had open heart for bypass and he went back to do cardiac rehab after not doing it at first. It made a big difference to him. The medical professionals/trainers at cardiac rehab bring you through increasingly more cardio and lifting and give you lots of counsel, all the time monitoring your heart and pulse.