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.