How is your son doing? I was hit with this about 15 months ago and my EF was 12%. I rebounded back to 65%. I do have some rib pain in my left side and my shoulder blades pop now as to were they did not before. I don't know if this is due to me having to slow my activity down to recover or if it is some symptons of the Myocarditis. Let me hear from you.
Myocarditis is an inflammatory disorder usually caused by a viral infection as you stated. Has there been a biopsy? It can be classified with biopsy into the following 3 types based on pathologic findings and an understanding for better prognosis.
Active myocarditis - Characterized by abundant inflammatory cells and myocardial necrosis
Borderline myocarditis - Characterized by an inflammatory response that is too sparse for this type to be labeled as active myocarditis; degeneration of myocytes not demonstrated with light microscopy. Your post seems to suggest phase.
Nonmyocarditis
If an active or borderline inflammatory process is found, follow-up biopsies can be subclassified into ongoing, resolving, or resolved myocarditis.
An EF of 50% is low normal and may not indicate any heart cell necrosis, but myocarditis generally results in a decrease in myocardial function (contractility of left ventricle), with an enlargement of the heart. Normally, the heart compensates for dilation with an increase in contractility, but because of inflammation and muscle damage, a heart affected with myocarditis is unable to respond to the increase in volume. This would be the worst case scenario if there is progresion.
Altho this needs to be watched periodically for a while, he is very lucky to have been diagnosed so early. :)