We report on a 9-year-old girl who developed signs of congestive heart failure with significant ascites due to constrictive pericarditis. Cardiac catheterization was performed to establish the diagnosis and to rule out restrictive cardiomyopathy. Endomyocardial biopsies were positive for activated macrophages and small-vessel disease, but no viral genomes were detected. Open pericardectomy was performed and histopathologic examination of the resected thickened pericardium showed extensive fibrosis and hyaline degeneration. A combined infection with parvovirus B19 (PVB19) and human herpes virus 6 (HHV6; subtype B) was proven within the resected pericardium. We suggest that local HHV6-induced immunosuppression enhanced the PVB19 infection, thus resulting in chronic infection and leading to constrictive pericarditis.