BACKGROUND Influenza viruses induce uncomplicated infections in most cases in individuals with no known predisposing factors. Acute febrile illness is generally limited to upper respiratory symptoms and several constitutional symptoms, including headache, lethargy, and myalgia. However, influenza A virus is a cause of severe morbidity and mortality worldwide. Some patients are at risk for serious and fatal complications. Cardiac involvement is a well-known condition, but, clinically apparent influenza myocarditis is not common. Few reports exist regarding recurrent fulminant influenza myocarditis. CASE REPORT We report here a fatal case of heart failure following myocarditis in a 14-year-old female who had seasonal flu symptoms but was otherwise healthy. H3N2 influenza virus infection was detected by molecular analyses of throat and nasal swabs, suggesting damage to myocardial cells caused directly by the virus. CONCLUSIONS Pericardial effusion myopericarditis may occur during influenza virus infection in young individuals, even those with no known predisposing factors. Physicians need to be aware that acute myopericarditis can be a fatal complication of recent influenza virus infection in all patients with instable hemodynamics. Early diagnosis and treatment could reduce, in some cases, the risk of severe cardiac events. However, this sudden and fatal outcome was difficult to predict in a healthy young female with no known risk factors.