supraventricular tachycardia
"I was diagnosed 6 years ago with Supraventricular tachycardia.  I am a 49 year old female.  Since that time I have been taking a 50 mg tablet of Toprol every other day.  I have had no other attacks since then and I used to get them about 5x a year.  Once in a while I can feel one coming on - my heart starts beating very fast - but apparently the Toprol is doing it's job because I have not had any attacks.  I am so thankful for this medication as I suffered for many years thinking I was going to die, my heart would be so hard and fast. One time I could actually see my chest moving and it went on for about 20 minutes."