Purpose and objectives: The ECG is an excellent tool to risk stratify patients with an acute myocardial infarction. However, little is known about the correlation within dynamic changes of ECG pre and post percutaneous coronary angioplasty (PTCA) and cardiovascular magnetic resonance (CMR) variables in patients with a first STEMI.Methods: In a prospective study, 85 patients with a first successfully reperfused STEMI, CMR was performed in the first week after PTCA. An ECG was recorded on admission, after PTCA and before patient's discharge. The sum of ST-segment elevation (SumSTE) and the percentage of ST-segment resolution were determined by 2 cardiologists. Successful ST-segment resolution (resSTE) was defined as ≥70% resolution compared to SumSTE before PTCA. Patients were divided into 3 groups: Group 1 (with resSTE after PTCA), Group 2 (no resSTE after PTCA but resSTE before discharge) and Group 3 (neither resSTE after PTCA nor before discharge). The left ventricular volumes, ejection fraction, area at risk, necrosis extension and microvascular obstruction were determined using CMR.Results: Overall, 46% of patients were in Group 1, 31% in Group 2 and 23% in Group 3. Mean time symptom-to-balloon was 3.8 ± 1 hour. There were no differences in the reperfusion time within groups. Patients in the group 1 showed smaller area at risk, end-diastolic and end-systolic volumes, myocardial necrosis, microvascular obstruction and higher ejection fraction compared to patients in groups 2 and 3 (Table 1).Conclusions: Dynamic ECG changes during hospitalization constitute an important tool for the risk stratification of STEMI patients successfully treated with PTCA. Non ST-segment resolution before discharge is an excellent predictor of adverse left ventricular remodelling.