The study will perform UC-MSCs transplantation in 2 groups and 1 control group with standard treatment. Each group consists of 5 subjects. In the first group UC-MSCs will be transplanted via intravenous (IV) route and the second group via intracoronary (IC) route. The IV group will receive 2 million cells/kg for each subject and the dosage of IC group is 50 million cells for each subject. All groups will be observed until 1 year.

Inclusion Criteria:

• STEMI patients within 5 days after symptom onset of a first ST-segment elevation myocardial infarction
• Have undergone successful percutaneous coronary intervention (PCI) with drug eluting stent implantation of the infarct-related artery and demonstrated hypokinesia or akinesia that involved more than two thirds of the LV anteroseptal, lateral, or inferior wall with LV ejection fraction of < 45% by echocardiography.
• Ability to understand and provide signed informed consent, or have a designated legal guardian or spouse legally able and willing to make such decisions on the subject's behalf,
• Willingness to attend all scheduled safety follow-up visits
• Subjects need to have a specific criteria of having a single vessel disease (ostial or proximal LAD vessels) that caused extensive anterior infarction (EF <45).

Exclusion Criteria:

• Hemodynamic instability as demonstrated by any of the following,
• Requirement of intra-aortic balloon pump of left ventricular assist device,
• Need for inotropic support (e.g. dopamine and/or dobutamine) for more than 36 hours for the maintenance of mean arterial blood pressure ≥ 60 mmHg,
• Previous or current concomitant serious illnesses, such as cancer, hematological disorders (Hb < 10 g/dL, WBC < 4 or > 11x109/L, or platelets < 100x109/L), kidney failure (creatinine level > 2.5 mg/dL, or creatinine clearance < 30 cc/min), serious infection or any other co-morbidities that could impact patient's short-term survival, psychiatric illness, history of drug of alcohol abuse,
• Prosthetic valves,
• Hypertrophic or restrictive cardiomyopathy,
• Women of child-bearing potential,
• Inability to comply with the protocol,
• Currently using implantable electronic defibrillator or pacemaker