This is a prospective, randomized, active control, single-blind, non-inferiority, multicenter clinical trial. 148 subjects will be registered at up to 10 Spanish sites. Subjects will be followed for 5 years.

All eligible patients (STEMI < 12 hours from onset of chest pain) will be randomized to

• Biotronik MAGMARISTM Sirolimus Eluting Bioresorbable Vascular Scaffold System (M-BRS) or
• Biotronik ORSIRO Sirolimus Eluting Coronary Stent System

Endothelium-independent vasomotor response (NTG injection) will be analyzed at 12 months angiographic follow-up (Primary endpoint).

In a subgroup of 40 patients Optical Coherence Tomography will be performed after the procedure and at 12 months follow-up.

Angiographic (QCA pre- and post-procedure and at 12 months follow-up), OCT data (at 12 months follow-up) will be analyzed off-line by an independent core lab.

Inclusion Criteria:

Clinical:

1. At least 18 years of age.

2. ST-segment elevation Myocardial Infarction documented in an ambulance or in a Cathlab, with ≥2 mm ST segment elevation in at least two contiguous leads, presenting in the Cathlab <12 hours after the onset of symptoms lasting ≥20 min requiring primary PCI.

3. Target lesion must be a de-novo lesion located in a native vessel.

4. The patient accepts Informed Consent

5. The patient understands and accepts clinical follow-up and angiographic control.

   Angiographic:

6. Vessel size should match available M-BRS scaffold sizes (≥2.75 mm, and ≤3.7 mm by visual assessment).

7. Lesion preparation by either manual thrombectomy or pre-dilatation has been successful, with opening of the vessel and TIMI ≥2 and residual stenosis <20%.

Exclusion Criteria:

1. Pregnancy.
2. Known intolerance to aspirin, heparin, stainless steel, sirolimus, and contrast material.
3. Distal vessel occlusion after recanalization
4. STEMI due to stent/scaffold thrombosis
5. Severe tortuous, calcified or angulated coronary anatomy of the study vessel that in the opinion of the investigator would result in sub-optimal m-BRS placement.
6. Fibrinolysis prior to PCI
7. Known thrombocytopenia (PLT< 100,000/mm3)
8. Active bleeding or coagulopathy or patients at chronic anticoagulation therapy
9. Cardiogenic Shock
10. Significant comorbidities precluding clinical/angiographic FU (as judged by investigators)
11. Major planned surgery that requires discontinuation of dual antiplatelet therapy.
12. Diffuse coronary artery disease that will require CABG
13. Chronic kidney disease with GFR<30 ml/min

Data on primary/secondary outcomes on individual basis may be shared with other researchers once main report as been published and review and approval of the research proposal by the steering committee of the Magstemi Trial

Data on primary/secondary outcomes on individual basis may be shared with other researchers once main report as been published and review and approval of the research proposal by the steering committee of the Magstemi Trial

Neither the participant ot the outcomes assessor will be aware of the treatment received. The patient will be blinded until the primary endpoint is reached (1 year follow-up).