I started having heart problems in December which made my resting heart rate around 115-140. Due to this I have not been able/allowed to exercise. Prior to this I was going to the gym 4 days a week and doing 40 minutes of hard cardio (180-200 hr). I talked to my doctor yesterday about if I could start exercising again and he said sure, once we can get my heart rate down to the 80s (current resting hr 100). However he said that once I do I need to go easy and not go over 140 heart rate. This is quite low considering what I'm used to.

As a note: My exercise goal is to burn calories. I need to do this so I can maintain my weight because I like to eat lol.

Anyways, my questions are: what exercises can I do that will not greatly increase my heart rate? Are there any forms of cardio I can still do that is a bit better than walking? Would lifting weights instead be good for me to do (I used to lift as well, but I'm not sure how much that impacts hr)?

Please, please, no yoga. I'm not flexible and I'm not into peaceful stuff.