supraventricular tachycardia
"Reading the mixed reviews here, the first thing that jumped out was people have problems swallowing.  This has happened to me quite a bit recently, using metroprolol succ ER 25 mg daily, for about 2 years now.  I did have great success in reducing my pulse (130 resting pulse for 20 years, adjust to 90 now).  Overall I was happy with it, but now somewhat concerned with long term use."