Atherosclerotic disease is responsible for one third of all deaths annually and is a major cause of comorbidities. While atherosclerosis is by itself a benign disease, it often leads to complications such as acute myocardial infarction with ST-segment elevation. Rescue angioplasty is indicated if thrombolytic therapy fails. However, the benefits in reducing mortality and the amount of myocardium effectively saved are not well established. The development of new tools, including cardiac magnetic resonance imaging to identify myocardial area at risk and infarcted increased diagnostic accuracy. However, unlike the context of primary angioplasty, little is known about the relation between coronary epicardial and microvascular flow after rescue angioplasty and myocardial salvage. The objective of this study is to evaluate whether there is a relation between these flows and myocardial salvage identified by Magnetic Resonance Imaging (MRI). At the end of this research, the investigators hope to contribute to a better understanding of coronary flow and its relation to the amount of heart muscle saved after rescue angioplasty. This is an important information that can help understand which cases benefit most from rescue angioplasty.

Inclusion Criteria:

• Patients with ST segment elevation myocardial infarction (STEMI) who underwent Thrombolysis within 12 hours of chest pain and present clinical and/or electrocardiogram (EKG) signs of failed thrombolysis with indication of rescue percutaneous coronary intervention (PCI).

Exclusion Criteria:

• Patients with contraindication to Cardiac Magnetic Resonance Imaging (MRI) (pacemaker, aneurysm clip, claustrophobia, hemodynamic instability, etc).
• Allergy or contraindication to Gadolinium.
• Contraindication to dual anti-platelet therapy.