Objectives: Galectin-3 (Gal-3) is involved in cardiac inflammation and fibrosis, and is in use as a biomarker that indicates increased risk in heart failure. This study examined the relationship between Gal-3 levels and acute and old myocardial infarction (MI) in patients assessed by cardiac magnetic resonance (CMR) imaging. Methods: Group 1 consisted of 38 patients with ST-elevation MI and single-vessel disease treated with primary percutaneous coronary intervention (PCI). Group 2 consisted of 52 patients with prior complicated MI. Twenty-two controls were included. CMR was performed in group 1 at 2 days, 1 week, 2 months and 1 year following PCI and in group 2 at >4 years after MI. Results: Median Gal-3 was elevated in patients compared with controls, group 1: 11.93 ng/ml (IQR 6.34-17.52, p = 0.03), group 2: 12.96 (IQR 6.33-19.29, p = 0.03) and controls: 10.16 (IQR 5.59-14.73). Gal-3 levels did not change during acute MI, and there was no relationship between Gal-3 and infarct size, troponin-T, high-sensitivity C-reactive protein, left-ventricular (LV) volumes or LV ejection fraction (LVEF) in group 1. In group 2, Gal-3 correlated modestly with MI size (r = 0.28, p < 0.05), LV end-diastolic volume index (r = 0.40, p < 0.01), LV end-systolic volume index (r = 0.43, p < 0.01) and LVEF (r = -0.39, p < 0.01). Conclusion: There was no relationship between Gal-3 levels and acute ischemic myocardial injury. A significant, modest relationship between Gal-3 levels, MI size and LV remodeling was only found in patients with old MI.