Atrial Fibrilation & medication side-effects

Approx. 1 month ago, I had a bout of atrial fibrillation, and it took 12 hours for my heart to return to a normal rhythm.  As a follow up regimen, I was put on 120 mg diltiazem once/daily, and 100 mg flecianide twice/daily.  Approx. 3 weeks into taking these meds, I began feeling a little short of breath.  I feel like I have to take deep breaths quite often throughout the day, and I'm wondering if this is a possible side-effect of these medications.

[Cleveland Clinic]

Flecainide has been known to cause shortness of breath.  The cardizem is less likely to be the culprit.  These symptoms typically go away after some time, but if they are really bothering you talk to you physician and consider switching to propafenone.