Cardiac resynchronization therapy (CRT) is underused. Recent guidelines have expanded indications for CRT to include less severe symptoms but now favor left bundle branch block morphology in patients with moderate QRS prolongation. The prevalence of CRT eligibility according to historical and current guidelines is uncertain. The aim of this review was to identify and synthesize all existing published research reporting the prevalence of CRT eligibility. A systematic review of electronic databases including MEDLINE, Embase, and the Cochrane Library was performed.