The Fontan procedure or total cavopulmonary connection (TCPC) is a standard palliative surgery for patients with complex single ventricle congenital heart anomalies. TCPC connects the inferior and superior vena cava (IVC and SVC) directly to the right pulmonary artery, bypassing the heart. The single ventricle is then reserved for pumping oxygenated blood to the systemic circulation. The Fontan procedure has benefited thousands of patients, but the Fontan circulation fails years later with relatively high mortality. The failing Fontan circulation causes end organ dysfunction due to venous blood congestion from elevated central venous pressure and low arterial blood perfusion from low cardiac output. The only effective option for the failing Fontan patient is heart transplant, but most of these patients are too sick to be transplant candidates. Cavopulmonary assist (CPA) is needed to pump venous blood from SVC/IVC through the Fontan connection to reverse failing Fontan pathophysiology. Our ultimate goal is to create a convenient and secure connection between the TCPC and the blood pump, establishing an ambulatory percutaneous CPA system. Our enabling technology is one of the world's most complex double lumen cannula (DLC). Through only one percutaneous venous cannulation, this DLC can easily connect the TCPC to a commercial blood pump without major surgery. This CPA system will bridge the failing Fontan patient to: 1) heart transplant, 2) recovery, and/or 3) further reconstructive heart surgery. In ou phase I study, the working prototype demonstrated up to 4.5 l/min blood flow in our sheep model and completely reversed failing Fontan circulation (n=5), achieving total CPA. In this Phase II SBIR, we will optimize the design based on our Phase I results, and fabricate a final commercial quality CPA DLC prototype for bench test and 5 day survival in vivo studies. Specific Aim 1: To design and fabricate a percutaneous DLC for ambulatory CPA application. Two thin membrane umbrellas are designed on the DLC to prevent infusion flow recirculation, ensuring efficient and reliable performance. These umbrellas do not block the blood flow from SVC and IVC to pulmonary artery, guaranteeing safety if the CPA system malfunctions. Two infusion openings guide separate blood flow to each umbrella, eliminating blood stagnancy and associated thrombosis formation. Particle image velocimetry (PIV) validated CFD will be used to optimize the design for maximum performance and minimal thrombotic potential. Specific Aim 2: To test the CPA DLC prototype in a simulated mock loop bench test. Bench testing will include performance/reliability evaluation, one month durability test, and PIV flow study. Specific Aim 3: To test the CPA DLC prototype in our TCPC sheep model. Short term in vivo studies (N=5) will test CPA DLC feasibility, performance, and reliability. Long term 5 day in vivo studies (N=8) will test performance, reliability, durability, and biocompatibility. Although the CPA DLC market is small, the impact on the patients that need CPA is significant.