Antiplatelet therapy with ticagrelor is currently indicated for treatment of patients presenting with acute coronary syndrome. Such therapy is started with the administration of a loading dose in patients which are not yet under treatment with P2Y12 inhibitors (antiplatelet agents). However it is unknown whether a loading dose is needed to maintain a satisfactory inhibition of platelet aggregation in patients who are already treated with a previous generation P2Y12 inhibitor (clopidogrel) during the passage to the newer compound ticagrelor. For this reason aim of the present study is to evaluate the levels of platelet aggregation during the pharmacological shift from clopidogrel to ticagrelor performed with or without a loading starting dose of the newer drug.

Inclusion Criteria:

• Acute Coronary Syndrome
• Current dual anti platelet treatment with ASA and Clopidogrel

Exclusion Criteria:

• No coronary revascularization within the previous six months
• Ongoing therapy with ticagrelor, prasugrel or ticlopidine before enrollment
• No treatment with glycoprotein IIb/IIIa inhibitors within the previous 6 days
• Patients which are known to be no responders to Clopidogrel
• Known neoplastic or autoimmune disease
• Liver cirrhosis
• Severe pulmonary disease
• Known disorder of Haemostasis
• Previous Stroke
• Ongoing pregnancy
• Therapy with any inhibitor of P450 Cytochrome until 15 days before enrollment
• Low platelet count or Hb<10 g/dl