This is an open label randomized pharmacodynamics study to compare platelet function reactivity of ticagrelor and clopidogrel after PCI in sub-set of patients who have undergone fibrinolysis at least 24 hour prior to PCI..A total of 70 patients will be enrolled. Prior to enrollment, patients have already undergone fibrinolysis (selected by the treating physician), aspirin (recommended dose 324 mg) on the first day and 81 mg daily thereafter, and Lovenox or heparin as per protocol of referring ER. Patients will undergo coronary angiography as standard of care and coronary stenting if indicated. Prior to angiography patient will be enrolled in this open label randomized protocol to receive clopidogrel or ticagrelor. Patients will be randomly assigned in a 1:1 ratio by open label study to receive either clopidogrel (Plavix, Sanofi-Aventis and Bristol-Myers Squibb; a 300-mg loading dose followed by 75 mg once daily) or ticagrelor (Brilinta, AstraZeneca; 180 mg loading and 90 mg twice daily) by a computerized system of randomization. Patients will receive clopidogrel or ticagrelor daily from enrollment to discharge. For patients who did not undergo PCI after enrollment, study drugs will be administered up to and including day 8th or hospital discharge, whichever comes first. Patients will be treated as per standard of care, and pharmacodynamics and pharmacokinetic study will be carried as per protocol. VerifyNow and VASP assay will be used to measure platelet reactivity for pharmacodynamic evaluation of ticagrelor vs Clopidogrel at specific time points: baseline (time 0), 30 mins, 1 hour, 2 hours, 8 hours and at 24 hours from first oral anti-platelet dose.. Blood will be collected from the sheath or ante-cubital vein into Vacutainer tubes for platelet function assay as below by VerifyNow and VASP. VerifyNow P2Y12 Assay: VerifyNow is a turbidimetric based system that measures platelet aggregation in the whole blood.8 This instrument measures an optical signal reported as P2Y12 Reaction Units (PRU). Vasodilator-Stimulated Phosphoprotein Phosphrylation (VASP) Assay: The measure of Vasodilator-Stimulated Phosphoprotein Phosphrylation (Biocytex Inc. Marseille, France), a method to quantify P2Y12 receptor reactivity, which reflects the extent of blockade of P2Y12 receptor blockade.9 Platelet reactivity index (PRI) is calculated by measuring VASP-P levels by mean fluorescence intensity (MFI) by stimulation with prostaglandin; PGE1and PGE1 plus ADP. PRI(%)=[(MFIPGE1)−(MFIPGE1+ADP)/(MFIPGE1)]×100%. ) Pharmacokinetic will be done at 30 min, 60 min, 120 min, 4 hours, 8 hours and at 24 hours. AUC from time 0-2 hours, Cmax at 2 hours, and Tmax at 2 hours for key secondary endpoint. Will collect Cmax and Tmax at all time points to be consistent, i.e. at 0, 30 min, 1 hour, 2 hour, 8 hours, and 24 hours when you draw PD measures at those time points and sample will be shipped.