Inclusion Criteria:  Patient between 18 and 90 years old Patient admitted to the acute or semi-recent phase (within the next fifteen days) of a myocardial infarction (primary or recurrent myocardial infarction) documented by a significant enzymatic release of troponin (threshold value at 100) in the course of: chest pain or shock, or flare-up of heart failure (left or global) or successfully resuscitated cardiac arrest, or paroxysmal ventricular arrhythmia with or without sus shift of the ST segment on the input trace, with or without Q wave of necrosis formed. This IDM may or may not be complicated by a more or less abundant pericardial effusion of more than 10 mm in the left parasternal, which may in the extreme be the cause of tamponade; Subject affiliated or beneficiary of a social security scheme; Patient having signed the free and informed consent.  Exclusion Criteria:  Patient with a pericardial detachment of less than 10 mm, or only systolic; Patient who had a break-in during the primary angioplasty guide or complicated coronary dissection extravasation with secondary pericardial effusion; Patient with advanced chronic renal failure Patient unable to perform an MRI (with a defibrillator or pacemaker). Known allergy to contrast agents, in particular gadolinium claustrophobic patient; Protected patient: adult under guardianship or other legal protection, deprived of liberty by judicial or administrative decision; Pregnant or breastfeeding woman; Patient hospitalized without consent.