“It depends” on ur circumstances.A-fib often presents in concert with other underlying health conditions, so the exercise prescription cannot be a one size fits all approach.
To follow some random exercise program off the internet could leave you face down and unconscious on the pavement while taking your afternoon walk!
Having said that, the good news is that you CAN exercise safely with atrial fibrillation. Have a detailed discussion with your cardiologist and medical management team and find out if there are any specific considerations that would preclude you from doing any certain types of activities.
If you were previously active, then you should let them know what your previous regimen was and what you’d like to achieve now after your diagnosis. Because the condition can reduce how much blood is ultimately reaching your exercising muscles, you will likely need to start off at a low level and then gradually increase your intensity and duration as tolerated.
A heart rate monitor “may” help you, but the inherent problem is that the numbers might jump around a bit with an irregular heart rhythms. The most prudent advice is to consult a clinical exercise physiologist with experience working with people with cardiac conditions.