Our tertiary care hospital serves a geographic region that includes approximately 800,000 children. During the past 3 years, there was an annual average of 2 cases of acute myocarditis due to suspected viral etiology, none of which had evidence of influenza infection. Within a 30-day period in October 2009, there were 3 cases of acute fulminant myocarditis and 1 case of acute perimyocarditis at Rady Children's Hospital–San Diego, all associated with confirmed H1N1 influenza A infection. There was serologic, echocardiographic, and/or histologic evidence of myocardial involvement in all cases (Figure 1A). Three children had echocardiographic evidence of an acutely decreased myocardial function. One child died likely due to acute atrioventricular block, as suggested by severe lymphocytic infiltration of the conduction system ((Figure 1)B to Figure 1D). Two children required extracorporeal membrane oxygenation support with gradual improvement of the ventricular systolic function over a 1-week period ((Figure 1)E and Figure 1F), which is typically observed in patients with fulminant myocarditis (2).