irregular heart

My brother is in the hospital with heart problems, with the little information I have I am looking for any possibilities of what the problem is since i havent been able to ind it on the net so far.  From what I understand his heart rate would be as slow as 30 bpm at some times, and as high as 160 bpm at other times.  I dont see how this would fall under any of the arrythmias i.e. v fib, v tach, v brad.  Also the docs are saying that they think it might have been cause by a virus, and the only information I could find on any viruses is Coxsackie B which can cause myocarditis, but this still dont seem consistent with the symptoms.  Any suggestions or ideas are greatly appreciated.