supraventricular tachycardia
"This by far has been the best medication (beta blocker) that has 100% kept my Atrial Tachycardia under control/and during an episode of A.T. Zero side effects for me at least. I have been on Lopressor for 30 years.  I have tried numerous other medications to control my arrhythmia, but Metroprolol is the best.  Tried Tenormin, which was okay for a while, but the side effects were too weird --fainting, numbness, cold extremities and I think it did something strange to my thought process."