Males develop increased myocarditis and progress to heart failure and myocarditis and dilated cardiomyopathy (DCM). Male and female BALB/c mice were inoculated intraperitoneally with 103 plaque forming units of heart passaged coxsackievirus B3 on day 0 and (A) myocarditis assessed histologically at day 12 post infection (pi) and (B) heart function (% ejection fraction) assessed by echocardiography at day 10 pi. An ejection fraction ≤45% indicates heart failure. (C) Dilation is observed in male hearts (right) but not in female hearts (left) in histology sections at day 35 pi. Magnification × 5. DCM was confirmed in males but not females at day 90 pi by echocardiography (data not shown). Data show the mean ± standard error of the mean of 7 - 10 mice per group. **, P < 0.01.