Abstract: Objective　To investigate the clinical features of fulminant myocarditis following an influenza A infection, to reduce misdiagnosis, and to improve early treatment and prognosis. Methods　The clinical data of two children with fulminant myocarditis caused by influenza A were retrospectively analyzed. Results　Both of the two cases were presented with acute onset. Patient 1 was a 14-year-old female who had seasonal flu symptoms with heart failure following myocarditis but was otherwise healthy. H3N2 influenza virus infection was detected by molecular analyses of throat and nasal swabs, serum cTnT was 29.5 ng/mL, CK-MB 20.3 ng/mL and Pro-BNP＞35000 pg/mL, with left ventricular dysfunction and ejection fractions 30%. Patient 2 was a 2 years and 10 months old male with the third degree atrioventricular block following myocarditis who had seasonal flu symptoms. H1N1 influenza virus infection was detected by molecular analyses of throat and nasal swabs, with left ventricular dysfunction and ejection fractions of 48%, cTnT 0.35 ng/ml, CK-MB 0.43 ng/ml, Pro-BNP 9740 pg/mL. He was given large doses of steroids and immunoglobulin therapy at the same time, and myocardial nutrition, anti-viral, correcting heart failure, and other comprehensive treatments were also given. He was discharged from hospital in good condition. One month later he developed clinical manifestations of cardiac insufficiency, and the whole 24 hours Holter showed the third degree atrioventricular block, then he was treated with permanent pacemaker implantation. After following-up for 6 months, he was in good condition. Conclusions Influenza A virus infection can cause myocarditis, which comprises a wide spectrum of cardiac involvement from mild myocarditis to cardiogenic shock. Fulminant myocarditis may occur during influenza A virus infection in young individuals, even those with no known predisposing factors. Physicians need to be aware that fulminant myocarditis can be a fatal complication of influenza virus infection in all patients with instable hemodynamics. Early diagnosis and treatment could reduce, in some cases, the risk of severe cardiac events.

Key words: influenza A virus;　fulminant myocarditis;　pericardial effusion;　atrioventricular block