The main goal of this clinical trial is to assess whether direct omission of aspirin after Percutaneous Coronary Intervention (PCI) with the continuation of ticagrelor monotherapy for 12 months versus 12 months ticagrelor plus aspirin is equally safe regarding the incidence of ischemic events in patients with ST elevation myocardial infarction (STEMI). Furthermore, the two treatment strategies will be compared regarding the incidence and extent of intramyocardial haemorrhage (IMH) and infarct size in the first week after PCI as determined with Cardiac Magnetic Resonance (CMR). The secondary efficacy endpoint consists of clinical bleeding events and all-cause mortality. The main analyses will comprise of clinical outcomes in the first three months after primary PCI and of CMR results. In addition, we will report on clinical outcomes at thirteen months.

Inclusion Criteria:

• Clinical and electrocardiographical diagnosis of STEMI
• Successful PCI (according to the treating physician) of the infarct-related vessel with a modern drug-eluting stent (DES)

Exclusion Criteria:

• Known allergy or contraindication for aspirin, ticagrelor or prasugrel.
• Previous PCI or MI less than 12 months ago
• Previous cardiac surgery
• Participation in another clinical cardiology study or study concerning platelet aggregation/ thrombosis. (unless the antithrombotic therapy prescribed in this other study will end due to clinical reasons (e.g. the STEMI))
• Pregnancy and breast feeding
• Concurrent use of oral anticoagulants (OAC)
• The periprocedural use of GPIIb/IIIa inhibitors
• Planned surgical intervention within 12 months of PCI
• Creatinine clearance <30mL/min or dialysis
• PCI of stent thrombosis
• Suboptimal stent result as judged by the interventional cardiologist.
• Life expectancy shorter than 13 months.
• Contra-indications for MRI or unable to undergo MRI (only applicable for the CMR subgroup population).