BACKGROUND: Guidelines recommend that patients with low ejection fraction (EF) after myocardial infarction (MI) have their EF reassessed 40 days after MI for implantable cardioverter-defibrillator (ICD) candidacy. This study examines rates of EF reassessment and their association with 1-year ICD implantation in post-MI patients with low EF. METHODS: We examined rates of postdischarge EF reassessment and ICD implantation among 10 289 Medicare-insured patients ≥65 years of age with an EF≤35% during the index MI admission from January 2007 through September 2010 in ACTION Registry-GWTG (Acute Coronary Treatment and Intervention Outcomes Network Registry-Get With The Guidelines). Multivariable Cox models tested the association between time-dependent EF reassessment and 1-year ICD implantation, stratified by revascularization status during the index MI admission. RESULTS: Among patients with EF ≤35% during the index MI admission, 66.8% (95% confidence interval [CI], 65.9-67.8) had EF reassessment within the next year. Revascularized patients were more likely to have EF reassessment (76.9% [95% CI, 75.8-78.0)] versus 53.7% [95% CI, 52.2-55.2]; P<0.001) and had shorter times to EF reassessment (median, 67 versus 84 days; P<0.001) than nonrevascularized patients. Among patients with EF reassessment, only 11% received an ICD within 1 year. Reassessment of EF was associated with a higher likelihood of ICD implantation for both revascularized (unadjusted, 12.1% versus 2.4%, P<0.001; adjusted hazard ratio, 10.6, 95% CI, 7.7-14.8) and nonrevascularized (unadjusted, 10.0% versus 1.7%, P<0.001; adjusted hazard ratio, 6.1, 95% CI, 4.1-9.2) patients. CONCLUSIONS: In US practice, EF reassessments are commonly performed among patients with MI with an initially reduced EF. Although 1-year EF reassessment is associated with increased likelihood of ICD implantation, 1-year ICD implantation rates remain very low even among patients with EF reassessment, regardless of revascularization status.