supraventricular tachycardia
"I have had palpitations for 18 years - it affected my life so badly that I eventually became agoraphobic for several years. I could do very little in the way of activity without having episodes. I was started out at 20mg a day and gradually work my way up to 80mg, but the 80mg caused me problems.  So I settled in at 40mg a day for many years until a few years ago.  I for some reason was having increased episodes in longer durations - at one point having continuous palpitations for 5 hours straight.  Not for the faint of heart. I ended up increasing my dosage to 60mg a day with no problems. 40mg and then 12 hours later 20mg. It seems to help and has also lessened the impact of those beats that feel like your heart is jumping out of your chest."