mitral valve prolapse
"I was diagnosed with Paroxysmal Atrial Tachycardia  in 1980 when I was 19 years old. Went to the ER, converted myself via Valsalva Maneuver -- went to my MD the next day/had an echocardiogram done and was diagnosed with Mitral Valve Prolapse. My heart throughout the day kept going into PAT (200+ BPM) No chest pain or anything, but pounding heart/fainting.  I was started on Lopressor at that time .... 100mg BID and this is an amazing drug. Sure I still get the odd PAT episode once in a while, but the pounding and skipped beats are greatly reduced. No side effects at all. It actually has a calming effect. Been on Lopressor for 35 years. Great antiarrhythmic."