BACKGROUND: Aldosterone antagonists (AldA) improve survival after myocardial infarction (MI) in patients with left ventricular systolic dysfunction (ejection fraction [EF] <40%) concomitant with either clinical heart failure (HF) or diabetes mellitus (DM). Although current American College of Cardiology/American Heart Association guidelines provide a class I recommendation for AldA therapy in such patients, how US practice reflects these recommendations is unclear. METHODS: Using data from the National Cardiovascular Data Registry ACTION Registry-GWTG, we describe contemporary discharge AldA prescription patterns among 202,213 patients discharged after acute MI from 526 US sites participating in ACTION Registry-GWTG between January 2007 and March 2011. RESULTS: Overall, 10.0% of patients were eligible for AldA without documented contraindication, with only 14.5% of eligible patients receiving AldA at discharge. Among the subset of AldA-eligible patients discharged on otherwise optimal medical therapy (68.9%), AldAs were prescribed to 16.1%. Aldosterone antagonist use was higher in patients with EF <40% and clinical HF with or without DM (17.7% and 16.6%, respectively), compared with patients with EF <40% and DM without clinical HF (7.8%, P < .001 for each). Fewer than 2% of participating centers used AldA in ≥50% of eligible patients. CONCLUSIONS: Despite clinical outcome evidence and class I guideline recommendations, AldAs are underused in the United States, with only 1 in 7 eligible patients prescribed AldA at discharge after MI. This contrasts with high use of other evidence-based post-MI medications and identifies a specific gap in translation of evidence into clinical practice.