['The participation of microRNAs (miRNAs) in cardiovascular diseases suggests them as potential targets for novel preventive and therapeutic strategies. In this study, the key myocardial miRNA, miR-21, was identified in the murine coxsackievirus B3 (CVB3)-induced myocarditis model and its contribution to disease progression was explored.', 'Myocardial microRNA expression changes in CVB3-infected mice were analyzed by real-time PCR and miR-21 was found to be the miRNA whose expression was significantly reduced. Mice were injected with plasmid encoding miR-21 (pMDH-miR-21) at day 1 post CVB3 infection and myocarditis severity was evaluated 7 days post-infection. The underlying mechanism of miR-21 in viral myocarditis was also investigated.', 'Myocardial miR-21 expression was negatively related to viral myocarditis severity. Recovery of miR-21 expression, by injecting with pMDH-miR-21, significantly relieved CVB3-induced myocarditis as shown by increased body weight, reduced myocardial injury, lowered myocarditis score and increased survival rate. Further study showed that miR-21 could protect myocardial apoptosis by specifically inhibiting its target programmed cell death 4 (PDCD4) expression.'] Does miR-21 confer resistance against CVB3-induced myocarditis by inhibiting PDCD4-mediated apoptosis?