Patients will be male or female aged 18 years and older who present to the emergency room (ER) < 6 hours from onset of AMI symptoms. The AMI must be confirmed by a 12-lead electrocardiogram (ECG) and documented in at least 2 leads. Each potential patient must be a candidate for primary PCI and not have thrombolytic therapy planned. To be eligible, patients must not have a prior history of ST-segment elevation MI.