Cardiac MRI provides very accurate assessment of LV function, such that small numbers of patients only are required to detect differences in LV function over time when comparing one group against another. The researchers are therefore comparing sequential cardiac MRI appearances and measurements in patients with acute MI and LV impairment at baseline (within 2 weeks of the acute MI), 3 months and 6 months. After the first MRI scan, patients are assigned to eplerenone or placebo in addition to usual secondary preventive therapy (double-blinded), which continues for 6 months, after which each patient's involvement in the trial is finished.