I had viral pericarditis in the Winter of 2007 while I was in my junior year of college. I had 1" of fluid built up around the medial side of my heart from continually running / racing on it for several weeks due to misdiagnosis. Inflamed bronchioles from running in the cold is what I was told I had, although I should have known better as I literally thought I was going to die most of the day, I didn't have good sense and at that time not running didn't seem like an option.
I took six months off and afterward was cleared to start running again. I started back VERY slowly and kept my heart rate under 130bpm and had success staying healthy during the summer months. However, once joined back with the team and started pushing it again the pericarditis returned almost immediately. This pattern reoccurred several times before the cardiologist convinced me to hang up my running shoes.
It is now 13 years after my first pericarditis attack and I am still plagued by it. While it wasn't active, my MRI showed latent myocarditis that was caused by a bad recurrent pericarditis episode at some point. With a wife and four active kids I want to be around and in decent shape for them as long as possible, so I started going to Cleveland Clinic to see Dr. Klien who is a world-leading expert in pericarditis / myocarditis.
In short, what I gleaned from Dr. Klien was that I should have taken 3+ years off of major (130+ bpm) cardio exercise with the amount of inflammation present to create 1" of fluid. Cardiac inflammation is extremely hard to calm down and can easily get agitated. It took out my personal favorite athlete Steve Ovett from high level running, it is no joke. (I wonder if Matt Centro has any lingering issues with his bout of pericarditis?)
In a nutshell, I had one of the best cardiologists in my whole region advising me in 2007 but he didn't have any experience with a healthy, very fit 22 year old with this condition who planned on returning to high-level competition.
Make sure you see someone who deals with this all the time. That will probably take going to a Mayo Clinic or Cleveland Clinic type of place. Myocarditis is more life-threatening than pericarditis and if you are just starting this journey you need experienced advice, I sure wish I would have had some of that...
If you choose to run, keep it super low key and sub 130bpm for a long long while!