['This study evaluated the regulation and function of micro-RNAs (miRs) in bone marrow-mononuclear cells (BMCs).', 'Although cell therapy with BMCs may represent a therapeutic option to treat patients with heart disease, the impaired functionality of patient-derived cells remains a major challenge. Small noncoding miRs post-transcriptionally control gene expression patterns and play crucial roles in modulating cell survival and function.', 'Micro-RNAs were detected by miR profiling in BMCs isolated from healthy volunteers (n = 6) or from patients with myocardial infarction (n = 6), and the results were confirmed by polymerase chain reaction (PCR) in a larger cohort (n = 37). The function of selected miRs was determined by gain-of-function studies in vitro and by locked nuclear acid (LNA) modified inhibitors in vitro and in vivo.', 'We identified several miRs that are up-regulated in BMCs from patients with myocardial infarction compared with BMCs from healthy controls, including the pro-apoptotic and antiproliferative miR-34a and the hypoxia-controlled miR-210. Inhibition of miR-34 by LNA-34a significantly reduced miR-34a expression and blocked hydrogen peroxide-induced cell death of BMC in vitro, whereas overexpression of miR-34a reduced the survival of BMCs in vitro. Pre-treatment of BMCs with LNA-34a ex vivo significantly increased the therapeutic benefit of transplanted BMCs in mice after acute myocardial infarction (AMI).'] Does micro-RNA-34a contribute to the impaired function of bone marrow-derived mononuclear cells from patients with cardiovascular disease?