The study will consist of a screening period, a 15±2 day treatment period, and a 7 day follow-up period. The screening period will be up to 7 days. Once each patient has signed the informed consent, the eligibility of the patient will be determined at screening, and laboratory assessments will be taken (Visit 1). During the treatment period, patients participating in the study will be randomized to receive either Ticagrelor with ASA, or Clopidogrel with ASA for 15±2 days. The final dose of study medication will be administered at the study site in the morning of day 15±2. Study visits at the beginning (Visit 2) and the end of the treatment period (Visit 4) will allow assessment of platelet function. At 7±1 days after Visit 2, a telephone visit (Visit 3) will be carried out for collection of information on concomitant medication, adverse events (including vascular events), and safety end point events. After the platelet function tests at Visit 4 are finished, patients in both groups will discontinue their study medication (end of treatment, EOT). A follow-up period will begin at 1 day after Visit 4 and continue for 7 days. During the follow-up period, patients in Ticagrelor group will take Clopidogrel 600 mg loading dose on the first day, followed by Clopidogrel 75 mg maintenance dose from the second day for 6 days; patients in Clopidogrel group will continue taking Clopidogrel 75 mg maintenance dose for 7 days. Both adverse events (including vascular events) and safety end point events will be collected at the safety visit (Visit 5), which will occur 7 days after Visit 4. The study will last approximately 4 weeks per patient. After the informed consents are signed by the patients, all adverse events (including vascular events), safety end point events and concomitant medications will be recorded at each visit.