Female, % 28 12.2 0.01 Diabetes Mellitus, % 11 4.9 0.15 Symptom onset to balloon time, min 172Ϯ64 161Ϯ61 0.27 Final corrected TIMI frame count 20.6Ϯ7.4 23.2Ϯ12.7 0.13 Final blush score 2 or 3, % 81.7 88.9 0.2 Relative ST segment resolution, % 72.8 [42.3, 85.3] 72.8 [57.7, 88.0] 0.56 LVEF change from baseline to follow-up, % 7.6Ϯ5.0 Ϫ3.0Ϯ4.1 Ͻ0.0001 Total stunning/remodeling score 2.5Ϯ3.1 0.5Ϯ2.3 Ͻ0.0001 5 day LVEF, % 45.4Ϯ9.6 49.1Ϯ9.2 0.01 30 day LVEF, % 52.9Ϯ10.8 46.1Ϯ8.9 Ͻ0.0001 5 day presence of MVO 52.5% (42/80) 59.5% (47/79) 0.37 5 day MVO, % of LV mass 0.30 [0.00, 1.67] 1.22 [0.00, 3.57] 0.06 5 day infarction, % of LV mass 21.1 [12.9, 29.2] 22.4 [12.9, 33.9] 0.28 5 day transmurality of infarction, % 71.9 [61.4, 79.6] 74.7 [65.9, 83.8] 0.08Conclusions: Smaller area of microvascular obstruction 5 days after primary PCI for STEMI predicts better recovery of regional and global left ventricular function.Background: Cardioprotective effects of human atrial natriuretic peptide (hANP) in patients with acute myocardial infarction (MI) have been suggested by randomized clinical trials, however, no reports used surrogate endpoints offered by cardiac magnetic resonance (CMR), the current gold standard imaging modality. We evaluated the effects of hANP on left ventricular (LV) function in patients with reperfused acute MI using CMR. Methods: Forty-nine patients with first-time acute MI reperfused with percutaneous coronary intervention were studied. Continuous intravenous infusion of hANP was initiated before reperfusion therapy and continued for at least 2 days in 21 patients (hANP group). The remaining 28 patients received no adjunctive pharmacological therapy (no hANP group). CMR was performed at the acute phase and after 6 months (6M) to evaluate infarct size, LV end-diastolic and end-systolic volume and LV ejection fraction (EF). Results: We observed no difference in age, gender, coronary risk factors, maximum levels of creatine phosphokinase, time to reperfusion and baseline CMR parameters between the 2 groups. However, at 6M, a significant improvement in LVEF in hANP group was seen compared to no hANP group (baseline: 48.1 Ϯ 11.4% to 6M: 52.8 Ϯ 10.6% vs. baseline: 49.9 Ϯ 13.6% to 6M: 50.0 Ϯ 10.7%; p ϭ 0.015). Conclusions: These results assessed using CMR suggest that intravenous hANP infusion can improve LV systolic function in patients with reperfused acute MI.