When you have a-fib, what is a good or safe heart rate when you exercise?

Atrial fibrillation : We like to control resting rate with a fib to 80 -ish. Exercise rate we try and tailor to the patient if they have a heart structural problem causing the afib. Generally tho not over140, but that again depends on the specifics for the patient.

Talk to your MD: Before you start, discuss it with your doctor. Normally, the good rule is the following: hr = (220 - age) x 0.8 for exercise heart rate. Best luck!