This paper briefly reviews the current guideline recommendations on the use of cardiac resynchronization therapy (CRT) devices in heart failure and focuses on the challenges that need to be addressed. Two essential issues are immediately apparent. The first regards encouraging implementation of evidence-based guidelines. The second concerns identifying the important gaps in evidence that exist with regard to patient selection and implantation techniques. In practice, clinicians must make decisions in evaluating patients for device implantation who do not fulfill the conventional criteria, but may still respond favorably with improvements in symptoms and outcomes. (...)