OBJECTIVES: We explored temporal trends in the use of aldosterone antagonist therapy among eligible patients with post-acute myocardial infarction (AMI) and reduced ejection fraction and characteristics associated with use in clinical practice. BACKGROUND: Current guidelines recommend initiation of aldosterone antagonist therapy post-AMI for patients with an ejection fraction ≤40% and heart failure or diabetes before hospital discharge, in the absence of contraindications. METHODS: Data from the American Heart Association's Get with the Guidelines-Coronary Artery Disease national database were analyzed for 81,570 post-AMI patients from 219 hospitals between 2006 and 2009, of whom 11,255 (13.8%) were eligible for aldosterone antagonist therapy. RESULTS: Among eligible patients, 1,023 (9.1%) were prescribed an aldosterone antagonist at discharge. Aldosterone antagonist use varied from 0% to 40% among hospitals. Patient and hospital characteristics independently associated with prescription of aldosterone antagonists were a history of diabetes, heart failure, coronary revascularization, and larger hospital size. Those with a history of kidney dysfunction, tobacco abuse, and higher ejection fraction were less likely to be prescribed an aldosterone antagonist. From 2006 to 2009, the use of aldosterone antagonists increased from 6.0% to 13.4% (p < 0.001). CONCLUSIONS: Although rates of aldosterone antagonist use are increasing slightly over time, the vast majority of AMI patients eligible for treatment fail to receive it at hospital discharge. The reason for this discrepancy between guideline-based therapy and actual prescribing patterns is unclear and should be further studied.