This trial aims to investigate the effects of the patient's own mesenchymal stem cells in the treatment of acute myocardial infarction. The trial is being conducted at the Severance Hospital, Yonsei University College of Medicine and several other centres in Korea in conjunction with Pharmicell Co Ltd. The trial proposes to enrol 135 participants with an acute myocardial infarction between December 2012 and January 2014. Participants will be randomly divided into three groups. A control group will receive conventional treatment only. One experimental group will receive a single injection of their own expanded bone marrow derived mesenchymal stem cells. While a second experimental group will receive two injections of their stem cells one month apart. Participants will be monitored for complications and changes in their clinical condition including changes in left ventricular ejection fraction (LVEF) as measured by MRI.