Most important cause of viral myocarditis is Coxsackie (picornavirus).

I think one giveaway in this question for Adenovirus versus Coxsackie virus is the shortness of breath when lying down (orthopnea). That can be a sign of dilated cardiomyopathy, which is most common after viral myocarditis with Coxsackie B infection (as per Sketchy).

picorna( coxsackie ) is more common than adenovirus but both can caause viral myocarditis