OBJECTIVES This study sought to ascertain the impact of heart failure (HF) guideline change on the number of patients eligible to undergo cardiac resynchronization therapy (CRT). BACKGROUND The 2013 HF guideline of the American College of Cardiology Foundation and American Heart Association (ACCF/AHA) narrowed the recommendations for CRT. The impact of this guideline change on the number of eligible patients for CRT has not been described. METHODS Using data from Get With The Guidelines-Heart Failure between 2012 and 2015, this study evaluated the proportion of hospitalized patients with HF who were eligible for CRT on the basis of historical and current guideline recommendations. The authors identified 25,102 hospitalizations for HF that included patients with a left ventricular ejection fraction (LVEF) ≤35% from 283 hospitals. Patients with a medical, system-related, or patient-related reason for not undergoing CRT were excluded. RESULTS Overall, 49.1% (n = 12,336) of patients with HF, an LVEF ≤35%, and no documented contraindication were eligible for CRT on the basis of historical guidelines, and 33.1% (n = 8,299) of patients were eligible for CRT on the basis of current guidelines, a 16.1% absolute reduction in eligibility (p < 0.0001). Patients eligible for CRT on the basis of current guidelines were more likely to have CRT with an implantable cardioverter-defibrillator or CRT with pacing only placed or prescribed at discharge (57.8% vs. 54.9%; p < 0.0001) compared with patients eligible for CRT on the basis of historical guidelines. CONCLUSIONS In this population of patients with HF, an LVEF ≤35%, and no documented contraindication for CRT, the current ACCF/AHA HF guidelines reduce the proportion of patients eligible for CRT by approximately 15%.