OBJECTIVE: To explore the molecular mechanism of micro ribonucleic acid-34a (miR-34a) in promoting the apoptosis of myocardial cells in the rat model of myocardial infarction (MI). MATERIALS AND METHODS: Sprague-Dawley (SD) rats were ligated with a left anterior descending branch to construct the MI model. The rats were randomly divided into four groups: sham operation group (Sham group), MI group, MI + miR-34a inhibitor group (MI + miR-34a antagomir group) and MI + miR-34a inhibitor negative control group (MI + antagomir NC group). Echocardiography (ECG) and magnetic resonance imaging (MRI) were adopted to detect the ejection fraction [EF (%)] and fraction shortening [FS (%)] of SD rats. Polymerase chain reaction (PCR) and Western blotting were used to detect expression levels of the apoptotic marker Caspase-3 and genes in Wnt/beta-catenin signaling pathway. Hematoxylin and eosin (H&E) staining was applied to detect cardiac injury. In in vitro experiments, the rat-derived myocardial cell line H9C2 was selected to simulate myocardial ischemia and hypoxia at the time of MI with an anoxic and serum-free injury model. C59, the Wnt/beta-catenin signaling pathway inhibitor was applied in MI + miR-34a antagomir + C59 group, and the effect of miR-34a on the apoptosis of myocardial cells through regulating the Wnt/beta-catenin pathway was measured with Real-Time quantitative PCR (qPCR) and 3-(4,5)-dimethylthiazol(-z-yl)-3,5-diphenyltetrazolium bromide (MTT) cell activity detection kits, respectively. RESULTS: It was found that after miR-34a antagomir reversed FS (%) and EF (%) in MI rats, the messenger RNA (mRNA) and protein levels of Caspase-3 in Sham group and MI + miR-34a antagomir group were significantly lower than those in the MI group (p < 0.05), indicating that the addition of miR-34a antagomir inhibited myocardial cell apoptosis after infarction, while the mRNA and protein levels of Wnt/beta-catenin were both higher than those in the MI group. Besides, H&E staining proved that miR-34a reversed the myocardial injury after MI. Similarly, in vitro experiments showed that, compared with those in Hypoxia group, the level of Caspase-3 decreased in Hypoxia + miR-34a inhibitor group and Sham group, while the apoptosis level in Hypoxia + miR-34a inhibitor + C59 group increased (p < 0.05). The results of the MTT assay were consistent with those of PCR. CONCLUSIONS: MiR-34a affects myocardial cell apoptosis by regulating the activation and inactivation of the Wnt/beta-catenin signaling pathway.