Idiopathic giant cell myocarditis (IGCM) is a rare cause of arrhythmia, heart failure and death in children. The etiology of IGCM is unknown. Endomyocardial biopsy and histological examination are essential for diagnosis. In our case, a one-month-old baby boy with no prior medical history died during breast-feeding. The gross autopsy and drug screen failed to disclose a cause of death. Hemotoxylen Eosin (H&E) stained cardiac tissue slides showed widespread and multifocal necrosis accompanied by mixed inflammatory infiltrate. Admixed with the infiltrate were fibroblastic proliferation and multinucleated giant cells in the absence of sarcoid like granuloma. Although myocarditis is usually thought to be a disease of older children, infants can also be affected. This entity can be the cause of some cases of sudden unexpected death in infancy.

Keywords: myocarditis, newborn