Myocardial infarction (MI) is a common cardiovascular disease with high mortality. The aim of the present study was to determine the biological role of miR-145 in MI rats and hypoxia-injured cardiomyocytes and to elucidate the potential mechanism. MI rats were induced by left anterior descending artery (LAD) ligation. qRT-PCR and western blot analysis were performed to determine the mRNA and protein levels, respectively. Compared with sham group, miR-145 levels in MI group were significantly decreased. We observed that lentivirus-mediated overexpression of miR-145 significantly improves cardiac function, reduces infarcted tissue size and prevents post-infarction induced apoptosis in rats after MI. Furthermore, PDCD4 was identified as a novel target of miR-145 in cardiomyocytes, and overexpression of PDCD4 could remarkably restore the miR-145-inhibited cardiomyocytes apoptosis and mitochondrial dysfunction after hypoxia injury. Therefore, our study indicated that miR-145/PDCD4 axis might be potential therapeutic targets for the treatment of MI, and its cardioprotective effect may be attributed to a reduction of mitochondria-mediated apoptosis.