Broadly:
Your cardiovascular risk needs to be formally assessed: i.e. what is the possibility that you will suddenly keel over of a heart attack whilst in charge of an aircraft? Having an episode of AF proves you to be higher risk than another otherwise identical individual.
Full assessment is likely to include resting ECG, echocardiogram (to assess for structural problems or signs of old heart attack), and possibly stress testing / imaging. You would also need your cholesterol and other blood work looking at.
You would be unfit to fly until this is all sorted, but as others have said, once the risk is properly assessed it's entirely possible to retain a valid medical.
Remember: ordinary cardiologists, unless qualified as an aviation medical examiner, are not in any position to comment on your suitability for flying.