Your question was posted a while ago - I hope things have resolved for you. I was put on metoprolol (12.5 mg) every 12 hours after my one brief afib episode. I was given the Rx in the ER and when I went to see my family doctor a few weeks later, he told me to stop it because of my asthma. He said since I had only been on it a short time at a low dose, I didn't have to taper it off but I did anyway, over a period of a week. I had a really tough time after I stopped it. When I was at rest, my heart rate and blood pressure where fine, but as soon as I stood up and started walking, my HR would shoot up to around 120-130. Going up stairs it could go as high as 140. I thought it was probably due to stopping the metoprolol so I wasn't too worried. (I was on a holter monitor at the time this was happening, so I figured if anything too bad was going on, the monitor would catch it.) I took it very easy during this time and after a week, my heart rate started returning to normal levels while I was active. While I was on the metoprolol, I noticed that after 10 hours the medication would start to wear off and my heart rate would begin to increase until I took the next dose. That's why I wasn't surprised when my heart acted a little wonky after I stopped it.