Corticoid Therapy in Acute Myocarditis

Patients will take intravenous administration of Methylprednisolone (500mg/100ml by IV over 30 minutes per day) for 3 days.

After intravenous administration of Methylprednisolone patients will take by oral Prednisone 1mg/kg per day once a day (with a maximum dose of 90 mg per day for patients weighing \> 90kg) for 1 month, followed with a progressive decrease of 10 mg Prednisone every 15 days until a dose of 10mg per day during 15 days (= stop).

Patients will take perfusion of placebo (G5%: 100ml over 30 minutes per day) for 3 days.

After the perfusion of placebo, patients will take by oral Prednisone placebo once a day for the same duration as that required if the patient was in the investigational medicinal products group (1 month + progressive decrease).