You need to talk to your cardiologist! Of course he knows your medical condition best, but I'll bet he'll say exercise will help keep the flutter from happening and being a couch potato will just weaken you. Exercise should help you keep your coronary arteries clear of plaque, which can lead to them closing up. But trust your doc, not us patients! I have lost weight, take my Crestor, and am trying to exercise more, and it's helping! White carbs, especially bread, are made into cholesterol by your liver.
I get supraventricular tachycardia, usually regular, just really fast, from eating certain foods that trigger it. For me it was almost always after eating certain meals. I worked with my allergist and kept a log of my foods and medicines for months, to find out what foods I am sensitive to. I now know which ones to avoid. My trigger foods also sometimes have given me coronary vasospasm.
My cardiologist has me keep atenolol on hand because it works faster and better for my arrhythmias than metoprolol. I also learned to do "Valsalva maneuvers" to break the arrhythmia. It usually works, but one time it went on for 5 hours and I had to get an adenosine conversion in the ER. I won't wait 5 hours again!