Transforming health care and outcomes for children with rare diseases is difficult within the current health care system. There is great variation in care delivery, inadequate and slow application of existing evidence, and ineffective use of available data to generate new knowledge. Individual care centers have inadequate numbers of patients for robust learning and improvement. In order to redesign the system, changes must take place at multiple levels, including the patient and family, clinician, practice and the network. The purpose of this project is to design, develop, and test further refinements to an improvement and research network focused on HLHS, the most severe congenital heart defect, and to use a registry to simultaneously improve clinical care, redesign care delivery systems and to conduct quality improvement, health services, outcomes, and comparative effectiveness research. The purpose of this initiative, specifically, is to improve care and outcomes for infants with HLHS by: 1) expanding the established NPC-QIC national registry to gather clinical care process, outcome, and developmental data on infants with HLHS between diagnosis and 12 months of age, 2) improving implementation of consensus standards, tested by teams, into everyday practice across pediatric cardiology centers, and 3) engaging parents as partners in improving care and outcomes. We utilize a quality improvement methodology, known as the adapted learning collaborative model, which expedites the implementation of tools and strategies that facilitate changes such as systematic care coordination, cardiovascular monitoring, and nutritional monitoring into every day practice. The NPC-QIC registry is used to document the impact of these changes on various care processes and outcomes (e.g., mortality rate, readmissions, and weight gain).