This is a research project grant (R01) application for Cardiac Biomarkers in Pediatric Cardiomyopathy. In this grant proposal, there will be three specific aims. The first will attempt to determine the clinical importance of established and novel cardiac biomarkers in children with newly diagnosed (incident) dilated cardiomyopathy. The second will aim to assess the clinical utility of cardiac biomarkers of collagen metabolism in determining the presence of myocardial fibrosis, as established by cardiac MRI, and diastolic dysfunction, as established by echocardiography in both newly diagnosed and existing cases of idiopathic or familial hypertrophic cardiomyopathy in children. The third and final aim will focus on determining whether longitudinal changes in cardiac biomarkers are associated with worsening heart failure class in clinically stable children with dilated or hypertrophic cardiomyopathy. These studies will significantly increase our understanding of pediatric cardiomyopathy, suggest new areas of research, and improve patient management as it relates to determining the most appropriate evidence-based clinical care for pediatric cardiomyopathy patients. PUBLIC HEALTH RELEVANCE: Cardiomyopathies (diseases of the heart muscle) are a leading cause of heart failure, death, and heart transplantation in children, yet time to transplan or death for children with cardiomyopathy has not improved during the past 35 years, with the most economically advanced nations having no better outcomes than developing nations. The percentage of children with cardiomyopathy who received a heart transplant has not declined over the past 10 years and cardiomyopathy remains the leading cause of transplantation for children over one year of age. The Cardiac Biomarker in Pediatrics R01 will aim to identify specific cardiac biomarkers and panels of biomarkers that will help determine the most appropriate evidence- based clinical care for pediatric cardiomyopathy patients, including when to consider heart transplantation as a therapeutic option, and will offer the least invasive (a particularly important consideration in children) and most-cost-effective approach to the early detection of cardiac dysfunction.