Since myocarditis is an inflammation of the heart muscle. There are various causes but it is usually caused by a virus. Depending on the cause and severity, symptoms and possible problems can range from no symptoms at all, to life-threatening heart failure. Many people with myocarditis recover completely but it can cause serious problems and even death in some cases.
Here's his medical report
Credits : myocarditis description : http://www.patient.co.uk/health/myocarditis-leaflet
picture : Sina Weibo