: Cardiovascular disease is the number 1 cause of morbidity and mortality in the United States. The most common manifestation of cardiovascular disease is myocardial infarction (MI), which can ultimately lead to congestive heart failure. Cell therapy (cardiomyoplasty) is a new potential therapeutic treatment alternative for the damaged heart. Recent preclinical and clinical studies have shown that mesenchymal stem cells (MSCs) are a promising cell type for cardiomyoplasty applications. However, a major limitation is the poor survival rate of transplanted stem cells in the infarcted heart. miR-133a is an abundantly expressed microRNA (miRNA) in the cardiac muscle and is downregulated in patients with MI. We hypothesized that reprogramming MSCs using miRNA mimics (double-stranded oligonucleotides) will improve survival of stem cells in the damaged heart. MSCs were transfected with miR-133a mimic and antagomirs, and the levels of miR-133a were measured by quantitative real-time polymerase chain reaction. Rat hearts were subjected to MI and MSCs transfected with miR-133a mimic or antagomir were implanted in the ischemic hearts. Four weeks after MI, cardiac function, cardiac fibrosis, miR-133a levels, and apoptosis-related genes (Apaf-1, Caspase-9, and Caspase-3) were measured in the heart. We found that transfecting MSCs with miR-133a mimic improves survival of MSCs as determined by the MTT assay. Similarly, transplantation of miR-133a mimic transfected MSCs in rat hearts subjected to MI led to a significant increase in cell engraftment, cardiac function, and decreased fibrosis when compared with MSCs only or MI groups. At the molecular level, quantitative real-time polymerase chain reaction data demonstrated a significant decrease in expression of the proapoptotic genes; Apaf-1, caspase-9, and caspase-3 in the miR-133a mimic transplanted group. Furthermore, luciferase reporter assay confirmed that miR-133a is a direct target for Apaf-1. Overall, bioengineering of stem cells through miRNAs manipulation could potentially improve the therapeutic outcome of patients undergoing stem cell transplantation for MI.