Patients (non-emergent) presenting for PCI will receive standard pre-procedural PCI care as outlined by the current ACC/AHA guidelines. Subjects will be consented peri- PCI (prior to or within 24 hours of PCI) and then randomized (1:1 ratio) to guide or standard non-guided (control) antiplatelet therapy. Physicians will be blinded to genotyping and platelet function results for subjects randomized to the standard therapy group for the duration of the study or if endpoint is met. Subjects on chronic clopidogrel or prasugrel therapy (≥ 2 weeks) will be guided by VerifyNow P2Y12 assay, whereas clopidogrel naïve subjects will be guided by Verigene CYP2C19 genotyping assay. Patients on clopidogrel maintenance and/or in the control group will also be genotyped; conversely, clopidogrel naïve subjects will have VerifyNow testing prior to discharge for additional study analysis. Patients in the guided therapy group that have a measurement of ≥ 230 PRU will be reloaded with 60mg prasugrel and receive standard maintenance dosing. Similarly, clopidogrel naïve subjects that are considered CYP2C19*2 carriers will also be reloaded with 60mg prasugrel and receive standard maintenance dosing (see flow schematic). Patients randomized to the control arm will remain on 75mg clopidogrel arm throughout the study. All patients will remain on 325mg ASA for one month and 81-162 mg daily ASA thereafter.