I too am on atenolol for tachy, pac's and pvc's. I live in Southeast Texas and it gets SUPER hot. I have a terrible time in the heat. It's been very cold here this week (those that get snow don't laugh, but upper 20's and lower 30's is very cold for us, and it is so damp here), and my PVC's just settled down this morning. They had been acting up since Monday. That's the longest I've noticed them being so constant. Like Jodie said, as long as the doctor ok'd the exercise, you're good to go.
I get pvcs and pacs. I work out 6 days a week with weights and I run 4 miles four times a week. If your doctor says it is okay then don't worry. I know that is hard. I ask my doctor all the time. He tells me to even go sky diving if I want. Ha! Fat chance.
I am on atenolol which is also a beta blocker. It seems to help me as well.
Heat and extreme cold will start my pvcs acting up. Don't know why. Again when I mentioned it to my doctor he just says "a lot of people tell me that".
Good luck.
Jodie