Hello. I am 62 years old 6 ft 2 inches tall and weigh 285 lbs. approx. 3 weeks ago I had a bout with afib. went to er and was sent home to take 25mg metraprolol half mornings and half evenings. when checking heart rate i went below 50 bpm and called my dr. He told me to wait a few days and use one quarter morning and evening and let him know if rate went below 55bpm. I totally stopped taking the med because my resting rate is usually between 51 and 55 bpm. I have no other side effects that I can tell. I was in afib for about 56 hours before it corrected itself. I am concerned about the heart rate. I have walked on tread mill this week and get rate up to 120-125 bpm but it goes back in the low fifties when setting or laying down.