Nesiritide Therapy to Preserve Function of the Left Ventricle After Myocardial Infarction

Inclusion criteria: * Patients with acute ST elevation myocardial infarction with \> or = 2 mm ST elevation in one or any combination of anterior leads, with successful revascularization (TIMI grade 3 flow) of the lesion within 24 hours of symptoms and consented within 24 hours of procedure. Exclusion criteria: * Cardiogenic shock or hypotension, Systolic BP\< 90 mmHg or overt Congestive Heart Failure (CHF) * Previous history of MI (Myocardial Infarction) * Previous ECG suggesting previous MI * Known Ejection Fraction (EF) \< 30% * Atrial fibrillation * Previously known significant valvular disease (Grade III, IV), cardiomyopathy and congenital heart disease. * Hemoglobin \<10 mg/dL * Pregnant women/nursing mothers * Participants still menstruating and have not been surgically sterilized must have a negative pregnancy test prior to participating in this study. * Unable to undergo cardiac MRI (Magnetic Resonance Imaging). * Contraindications to MRI include pacemaker or defibrillator, pregnant women, atrial fibrillation or other arrhythmia, cerebral aneurysm clips or severe claustrophobia.