I have had atrial fibrillation for 3 years now and have been on bisoprolol all this time. It always made me feel so tired. I have had 4 episodes last year which were awful and ended up in a&E. My cardiologist has just changed my bisoprolol for flecainide and Adizem . I have been taking them for a week and yesterday went into A fib again. Cardiologist has now increased Felcainide dose from 50mg twice daily to 100mg twice daily. I am hoping this will help but finding that I am now suffering with constipation. Has anyone else had this problem?