Arterial thromboembolic disease is rapidly becoming the new epidemic of pediatric tertiary care centers due to an increase in invasive monitoring, life saving technologies such as ECMO, and new surgical techniques and graft materials used to repair complex congenital heart lesions. Yet, therapeutic options for preventing or treating this life and limb threatening disorder are limited. Major obstacles to drug development include: (i) A deficiency in knowledge of the extent to which platelets from neonates, infants, and children can form thrombi in injured blood vessels, (ii) limited information on the ability of various agents to curtail pediatric platelet- mediated adhesion and activation under physiologically relevant conditions, and (iii) a lack of sophisticated technologies that permit rapid assessment of pediatric platelet responses to agonists and antagonists in a high-throughput manner using a minimum quantity of blood. To address these clinically relevant issues, low volume microfluidic devices and high throughput screens (HTS) will be used to predict platelet responses to multiple combinations of agonists as well as antagonists, while a novel biological platform will be used for the in vivo assessment of drug efficacy in the prevention of pediatric platelet-mediated thrombosis. Critical questions to be addressed include: Can sophisticated technologies be developed that permit rapid assessment of pediatric platelet responses to agonists and antagonists in a high- throughput manner using a minimum quantity of blood? Can novel agents be identified for future development or use? Are there age related differences in function that would preclude the use of specific anti-platelet agents in certain subsets of pediatric patients? Can a small animal model be developed to better assess pediatric platelet responses to anti-thrombotic agents? Can in vitro assays be predictive of drug efficacy in vivo? Ultimately, we believe the work outlined in this proposal will lead to a better understanding of the appropriate class of anti-platelet agent to use for at risk pediatric patients. Moreover, it may be possible to define the feasibility and enrollment criteria for future clinical trials to test the diagnostic utlity of our in vitro approaches. The proposed work is also relevant to the mission of the agency, which is to encourage translational and collaborative research to advance our knowledge of underlying mechanisms of drug action and response in children at various developmental stages.