This case study is in press in the Journal of Clinical Virology. The virus was not found in the heart on biopsy; only post-mortem on autopsy. A fatal case of Human Herpesvirus 6 chronic myocarditis in an immunocompetent adult Nicolas Leveque a,? , Camille Boulagnon b , Camille Brasselet c , Franc ? ois Lesaffre c , David Boutolleau d , Damien Metzc, Paul Fornesb, Laurent Andreolettia a Clinical and Molecular Virology Unit, University Hospital and EA-4303 Faculty of Medicine, Reims, France b Pathology Department, University Hospital, Reims, France c Cardiology Department, University Hospital, Reims, France d Virology Department, Piti-Salptrire University Hospital, AP-HP and UPMC Univ Paris 06, ER1 DETIV, Paris, France Background: Human Herpesvirus 6 (HHV-6) is an important cause of fulminant or acute viral myocarditis in immunocompromised or immunocompetent patients. However the physiopathological mechanisms of HHV-6 related acute myocarditis and the involvement of subsequent HHV-6 reactivation phases in the development of chronic cardiomyopathies remain to be assessed. Objectives: To describe a case of fatal HHV-6 chronic myocarditis in an immunocompetent adult. Study design: Case report and detailed histological and viral diagnoses by combination of histol- ogy/immunohistochemistry and polymerase chain reaction techniques on cardiac tissues. Results: Histopathological analysis of ventricular tissues showed large interstitial and scarring fibrotic areas with a moderate mononuclear cell infiltrate compatible with histological aspect of chronic myocarditis. Detection of both HHV-6 by real-time PCR and viral glycoproteins in mononuclear and endothelial cells by immunohistochemistry evidenced an ongoing cardiac HHV-6 replication with viral late protein synthesis activity. Conclusions: This case report indicates that HHV-6 can establish a chronic active myocarditis leading to heart failure in immunocompetent subjects. ???