When a patient has a heart attack, a blockage occurs in a coronary artery that delivers oxygen to the heart muscle. The heart muscle may weaken, causing heart failure. The body naturally makes a protein called insulin-like growth factor-1 (IGF-1) that may protect the heart muscle cells from dying and may prevent heart failure or lessen the damage that occurs. IGF-1 is also available as a drug called mecasermin. In this study, heart attack patients will be given either a dose of mecasermin or a placebo (inactive treatment) after their coronary artery has been opened by a stent. The purpose of the study will be to evaluate the safety of the therapy and to test if the therapy will prevent or lessen heart failure by evaluating a cardiac magnetic resonance imaging (MRI) taken one day and eight weeks after the heart attack.

Inclusion Criteria:

• Age 18 - 75
• Presents within 2-12 hours of at least 30 minutes of myocardial ischemic pain
• ECG evidence of myocardial infarction
• Undergoing percutaneous coronary intervention (PCI) for ST-elevation myocardial infarction
• Left ventricular ejection fraction during PCI of 40% or less
• TIMI flow grade 3 in the infarct-related artery following reperfusion and stenting

Exclusion Criteria:

• History of prior myocardial infarction
• Prior history of heart failure, left ventricular dysfunction or cardiomyopathy
• Active or suspected neoplasia
• Known impaired liver function
• Cardiogenic shock
• Estimated glomerular filtration rate < 45 ml/min/1.73m2
• History of hypoglycaemia requiring hospitalisation
• History of primary insulin-like growth factor-1 deficiency or growth hormone disorders
• Contraindication to cardiac magnetic resonance imaging
• Pregnancy or nursing mothers
• Known allergy to study drug or any of its inactive ingredients
• Treatment with another investigational agent within 30 days of enrolment
• Subjects unable or unwilling to comply with follow-up requirements of study
• Subjects unable to provide written informed consent