What do I do about exercise?

I have been diagnosed with SVT and PVCs...I often experience prolonged episodes of SVT where my heart goes from normal to 250+ bpm and down to 40 bpm and then back to normal.  I am taking Metoprolol 50 mg twice daily.  My cardio merely said to go ahead and exercise and "see what happened".  If I don't "tolerate" it, we'll do more testing.  I'm afraid to start exercising.  I don't like the chest pain, dizziness, fatigue, or other symptoms I experience with these episodes.  I've already had a stress echo and Holter test.  What would be next?  I see my cardio again on the 22nd.  What do I need to ask/tell them?  Do I just start exercising before I go and pray I don't end up in the ER a 4th time?