Is It Safe To Exercise While Being Diagnosed With Atrial Fibrillation?

I was diagnosed with atrial fibrillation three months ago and the cardiologist is trying to stabilize the high heart rate that goes with the irregular heartbeat. A physical therapist has been a bit overboard on exercises given to me for another problem. I find my A. Fib hits hard afterwards.The therapist also puts a very hot heating pad on my injured back. Do these two treatment for the back affect the A. Fib?