This study is a randomized, double-blind, multi-center study designed to compare differences in rates of myonecrosis (measured as an elevation of CK-MB ratio ≥ 2 times ULN) within 24 hours following low-medium risk percutaneous coronary intervention (PCI) in aspirin or clopidogrel non-responsive patients who are randomized to heparin with or without eptifibatide therapy during PCI. All subjects must also be pretreated with clopidogrel (300-600 mg) at least 2 hours before PCI. Study subjects will be randomized to either eptifibatide and unfractionated heparin or unfractionated heparin and placebo. Study subject randomization in aspirin non-responsive patients will be stratified based upon clopidogrel responsiveness.