I'm gonna get the usual 'Why are you asking this on an internet forum?', of course , but the thing is I've already spent many 100's of $AU on going to the Doc's, having loads of tests and seeing various specialists, just to be told eventually "Take the tablets, you'll be fine".
So you've consulted the medics, and they've told you you're OK – which isn't what you want to hear, so you're coming on the forum in the hope we'll tell you something different??
A lot of people (me included) have occasional heart flutters.
You've had bloods, ECG, Echo etc – what else would you like them to do? Crack you open to take a look?
Forum diagnosis: You're going to DIE IMMINENTLY.
Print this out and take it to the hospital NOW, it should get you the REAL diagnosis, not the fake one they've been fobbing you off with all this time. :-)