To examine the efficacy of chewing Ticagrelor versus Prasugrel in ST-elevation Myocardial Infarction (STEMI) patients on platelet reactivity.

Inclusion Criteria:

1. Patients presenting with STEMI
2. Informed, written consent

Exclusion Criteria:

1. Age < 18 years or Age > 75 years
2. Active bleeding; bleeding diathesis; coagulopathy
3. Increased risk of bradycardic events
4. History of gastrointestinal or genitourinary bleeding <2 months
5. Major surgery in the last 6 weeks
6. History of intracranial bleeding or structural abnormalities
7. Suspected aortic dissection
8. Any other condition that may put the patient at risk or influence study results or investigator's opinion (severe hemodynamic instability, unconsciousness, known malignancies or other comorbid conditions with life expectancy <1 year)
9. Administration in the week before the index event of clopidogrel, ticlopidine, prasugrel, ticagrelor, thrombolytics, bivalirudin, low-molecular weight heparin or fondaparinux.
10. Concomitant oral or IV therapy with strong CYP3A inhibitors or strong CYP3A inducers, CYP3A with narrow therapeutic windows
11. Known relevant hematological deviations: Hb <10 g/dl, PLT<100x10^9/l
12. Use of coumadin derivatives within the last 7 days
13. Chronic therapy with ticagrelor, prasugrel, clopidogrel or ticlopidine
14. Known severe liver disease, severe renal failure
15. Known allergy to the study medications
16. Pregnancy
17. Human immunodeficiency virus treatment
18. The use of IIBIIIA receptor antagonists in the 48 hours before enrollment (if abciximab use then in the last 14 days).
19. If the patients cannot sign percutaneous coronary intervention (PCI) informed consent for any reason.