ALK-negative CD30-negative peripheral T-cell lymphoma (PTCL) is an exceedingly rare neoplasm in children. Equally rare is the finding of cardiac involvement from lymphoma at presentation. The authors present a pediatric patient with PTCL involving the heart. The patient had orthopnea and an abnormal echocardiogram on presentation. After three doses of radiation, he died, and the autopsy showed massive infiltration of the heart and cardiac vessels by tumor. The authors review briefly the biology of PTCL and the incidence of cardiac involvement with lymphoma, which is not often appreciated prior to death.