I've been running for over 40 years. I am a health professional. No cardiovascular issues. iMO many physicians really don't know what they are talking about re exercise and diet and will generally be conservative with advice. Arrhythmias can also be induced by many other factors as well ie hydration, electrolyte imbalances, etc. I would recommend going to an exercise physiologist who knows what they are doing and work out a plan with them.