 The aim of this study is to evaluate the effectiveness and safety of adjunctive eptifibatide during primary PCI in patients presenting to the catheterization laboratory within 12 hours of symptom onset. The primary objective of this randomized clinical trial is to examine the safety and effectiveness of the addition of eptifibatide therapy immediately prior to or at the time of PCI in patients presenting with a STEMI for primary PCI who have not received up-front glycoprotein IIbIIIa inhibitor therapy. The secondary objective of this clinical trial is to assess effectiveness of adjunct eptifibatide therapy with respect to the following endpoints: 