The American College of Cardiology (ACC) and the American Heart Association (AHA) have provided leadership in enhancing the quality of cardiovascular care, including the development of clinical performance measures and clinical registries that permit the evaluation of quality of care and stimulate quality improvement. Compliance with ACC/AHA performance measures and metrics encourages the provision of the strongest evidence-based quality of care, including therapies that are life-extending or life-enhancing. Among quality metrics, only a subset should be considered performance measures-that is, those measures specifically suitable for public reporting, external comparisons, and possibly pay-for-performance programs, in addition to quality improvement. These performance measures have been developed using ACC/AHA methodology, often in collaboration with other organizations, and include the process of public comment and peer review. Quality metrics are those measures that have been developed to support self assessment and quality improvement at the provider, hospital, and/or health care system level. These metrics represent valuable tools to aid clinicians and hospitals in improving quality of care and enhancing patient outcomes, but may not meet all specifications of formal performance measures. These quality metrics may also be considered "candidate" measures that with further research of field testing would meet the criteria for formal performance measures in the future. This measure classification is intended to aid providers, hospitals, health systems, and payers in identifying those measures that the ACC and AHA formally endorse as performance measures, while at the same time promoting the broader range of clinical metrics that are useful for quality improvement efforts.