This is an observational, prospective, multicenter study (12 hospitals belonging to the Italian Cardiology Network) in patients with STEMI ST elevation myocardial infarction (STEMI) treated successfully with primary percutaneous coronary intervention (PCI), that will be followed for 12 month after the acute event, in order to ascertain the predictive value of myocardial viability measured with cardiac magnetic resonance (1.5 T; based on the transmural distribution of late enhancement in the infarcted segments) for the identification of left ventricular (LV) remodelling (REM) 6 months after STEMI.

The present study is divided into 3 appointments following the standard inpatient stay for the index event (STEMI).

T0: Inpatient stay for index STEMI. Assessment of eligibility for participation in the study:

• STEMI diagnosis
• Primary PCI
• Confirmation at second-day transthoracic echocardiogram and pre-discharge echocardiogram of left ventricular dysfunction
• Biomarker assay

Visit 1 (V1): between 30 and 40 days post-STEMI. Clinical evaluation and performance of cardiac MRI with paramagnetic contrast agent (gadolinium) for measurement of infarct territory size and myocardial viability.

Visit 2 (V2): 6 months after STEMI. Clinical evaluation and second cardiac MRI, without contrast medium, for measurement of left ventricular volumes and consequently for measurement of the presence of adverse left ventricular remodeling.

Visit 3 (V3): 12 months after STEMI. Clinical re-evaluation with collection of data regarding events of interest for secondary endpoint. Performance of transthoracic echocardiogram.

The examinations and follow-up visits included in this study are part of clinical practice for treatment and risk assessment in patients who suffered STEMI with the exception of cardiac MRI without contrast medium at 6 months.

Cardiac magnetic resonance (CMR) data (1 month and 6 months) will be centrally analyzed post hoc at the MRI center.

Inclusion Criteria:

• Patients with STEMI (first episode) (defined according to European Society of Cardiology Guidelines 2017) with symptom onset within 12h (Class I), or >12h <48h (Class IIa), successfully treated by primary PCI.
• Patients with regional systolic dysfunction of 2 or more adjacent segments of the left ventricle, in the territory of the culprit artery, documented by echocardiogram on day 2 (Echo1) and confirmed at pre-discharge follow-up (Echo2).

Exclusion Criteria:

• Patients with documented prior myocardial infarction. In the event that cardiac MRI examination performed one month after STEMI shows areas of late enhancement even in segments of the left ventricle other than those subtended by the culprit artery, the patient will be allowed to continue the study if he or she does not have significant left ventricular dilatation and has no symptoms of heart failure;
• Patients with known cardiomyopathy;
• Patients with malignant neoplasia or systemic pathology with a "quoad vitam" prognosis of less than 1 year;
• Patients with known active infectious disease;
• Patients who are unable to express valid informed consent at the time of enrollment;
• Patients with specific contraindications to the performance of cardiac MRI, including:

Wearers of non-resonance-compatible devices; Previous surgery with placement of non-resonance-compatible vascular clips Claustrophobic patients; Patients with allergies and/or other specific contraindications to the use of paramagnetic contrast agents (gadolinium).

Consecutive patients with acute ST-segment elevation myocardial infarction (STEMI) treated with effective primary angioplasty (PCI)