Originally Posted by Honez

As someone with heart issues, I agree. Please go see a cardiologist. It could be nothing, it could be a mitral valve prolapse (which is very common in women) or a number of things. Get yourself peace of mind. The tests they will run on you are not painful at all. They will most likely do a stress test since you seem to be having this problem when you work out. You will get to walk on a treadmill as they keep cranking it up while you are attached to a heart monitor to see if they can replicate the irregular heartbeat. They may also do an Echocardiogram which is just an ultrasound on your heart (that is actually kind of cool to watch).

Good luck to you and please, let us know how things go.