Objective: To determine the safety and diagnostic accuracy of adenosine-stress cardiac magnetic resonance (CMR) perfusion imaging early after acute ST elevation myocardial infarction (STEMI) compared with standard exercise tolerance testing (ETT). Design and setting: Cross sectional observational study in a university teaching hospital. Patients: 35 patients admitted with first acute STEMI. Interventions: All patients underwent a CMR imaging protocol which included rest and adenosine-stress perfusion, viability, and cardiac functional assessment. All patients also had an ETT (modified Bruce protocol) and x ray coronary angiography. Main outcome measures: Safety and diagnostic accuracy of adenosine-stress perfusion CMR vs ETT early after STEMI in identifying patients with significant coronary stenosis (>70%) and the need for coronary revascularisation. Also, to determine if CMR can distinguish between ischaemia in the peri-infarct zone and ischaemia in remote myocardium. Results: CMR imaging was well tolerated (all patients completed the protocol) and no complications occurred. CMR was more sensitive (86% vs 48%, p = 0.0074) and more specific than ETT (100% vs 50%, p,0.0001) for detecting significant coronary stenosis, and more sensitive for predicting revascularisation (94% vs 56%, p = 0.039). Inducible ischaemia in the infarct related artery territory was seen in 21 of 35 patients and was associated with smaller infarct size and less transmurality of infarction. Conclusions: Adenosine-stress CMR imaging is safe early after acute STEMI and identifies patients with significant coronary stenosis more accurately than ETT. D espite the evidence in favour of primary percutaneous coronary intervention, the majority of patients presenting with acute ST segment elevation myocardial infarction (STEMI) are still treated with intravenous thrombolysis. Because of the relatively high incidence of failed reperfusion and the occurrence of reocclusion, guidelines recommend that following intravenous thrombolysis for STEMI patients with high risk features (such as an ejection fraction less than 0.40, recurrent ischaemia, presence of shock or severe pulmonary congestion) should undergo in-hospital cardiac catheterisation.3-7 Other patients should have an exercise tolerance test (ETT) in the hospital or early after discharge to assess the presence and extent of inducible ischaemia (class 1 evidence), or a stress imaging study if baseline ECG abnormalities compromise interpretation of the ETT.7 However, although widely available and cost-effective, ETT has important and well known limitations in terms of diagnostic accuracy. [8][9][10] Cardiac magnetic resonance (CMR) imaging is becoming increasingly available for the assessment of patients with coronary artery disease. CMR allows a simultaneous assessment of myocardial perfusion, function, and scar at high spatial resolution. [11][12][13] In patients with recent STEMI, late gadolinium enhanced CMR imaging already provides detailed information about the extent of the myocardial sca...