Myocarditis is caused frequently by viral infections of the myocardium. In the past, enteroviruses (EV) were considered the most common cause of myocarditis in all age groups. Other viruses that cause myocarditis are adenovirus and influenza viruses. Parvovirus B19 infection is associated sometimes with myocarditis. Members of the Herpesviridae family, cytomegalovirus (CMV), and human herpesvirus 6 (HHV-6) have been associated occasionally with myocarditis. During an atypical outbreak of acute febrile syndrome, eight children, with ages from 5 months to 15 years, died in cardiogenic shock due to myocarditis in July-August 2005, in the city of Havana, Cuba. Nested polymerase chain reaction (nPCR) and nested reverse transcription-PCR (nRT-PCR) were carried out on fresh heart muscle and lung tissue to analyze the genomic sequences of adenovirus, CMV, HHV-6, herpes simplex virus, Epstein-Barr virus (EBV), varizella zoster virus, influenza virus A, B, C, respiratory syncytial virus (RSV) A and B, parainfluenza viruses, rhinoviruses, coronavirus, flaviruses and enteroviruses. Evidence was for the presence of the adenovirus genome in 6 (75%) of the children. Phylogenetic analyses of a conserved hexon gene fragment in four cases showed serotype 5 as the causal agent. No others viruses were detected. Histological examination was undertaken to detect myocardial inflammation. After exclusion of other possible causes of death, the results indicated that viral myocarditis was the cause of death in patients with adenovirus infection.