- OR people who have had a ST elevation heart attack will be excluded for at least 72 hours post-heart attack and until cardiac enzymes return to normal. People who have had a non-ST elevation heart attack will be excluded if they have evidence of ongoing ischemia, defined as chest pain or new electrocardiogram (ECG) changes in the 12 hours prior to study entry and/or rising creatine kinase (CK) and CK-MB serum enzymes.