ABSTRACT This Phase II STTR application from Caeli Vascular, LLC entails a 24-month period focused on further development of a novel multi-modal venous thrombectomy device. The PI is a vascular surgeon with biomedical research and entrepreneurship experience, and is supported by a team of highly qualified investigators, including a vascular biologist, neurosurgeon, veterinarian, biomedical engineer, mechanical engineer, and a team of marketing and management experts. The primary objective of this application is to build on successful Phase I feasibility studies, and further develop the Hydra Catheter Thrombectomy System technology to address all current gaps in the state of the art for the treatment of large-volume deep venous thrombus (DVT). Each year, more than 900,000 Americans will develop a large-volume DVT, and up to 100,000 of these will die as a result of a complication within 2 weeks of diagnosis. Treatment options of large-volume DVT are limited, and currently available percutaneous endovascular thrombectomy devices have various shortcomings that impact treatment efficacy and safety. Major gaps include increased risk of intra-procedural thrombus embolization leading to a pulmonary embolus (PE), systemic leak of chemical thrombolytic medication leading to increased risk of bleeding, risk of vein wall and valve trauma leading to chronic impairments, and inability to completely remove thrombus leading to unresolved DVT. To address all the gaps in the state of the art of percutaneous venous thrombectomy devices we designed and prototyped the Hydra Catheter Thrombectomy System. Unique and proprietary features of the device include adjustable ecapsulation balloons, an infusion catheter segment to facilitate localized and judicious delivery of chemical thrombolytics, a rail-mounted leaflet agitator that does not engage the vein wall, and mechanism for isovolumetric suction and infusion to facilitate flushing of thrombus fragments and thrombolytics from the venous treatment zone. Phase I studies demonstrated the feasibility of the device to prevent distal microembolization, prevent vein wall collapse and over-distension, and achieve effective removal of luminal thrombus in an ex vivo flow system. In this Phase II study, our team will further develop key component of the device and evaluate the efficiency of the technology ex vivo and in vivo with the following specific aims: Aim 1: Develop and test a newer generation Hydra Pump to facilitate isovolumetric suction and infusion through the Hydra Catheter Thrombectomy System in an ex vivo flow system. Aim 2: Evaluate Hydra Catheter Thrombectomy System efficacy and preliminary safety in a validated in vivo porcine vena cava DVT model By completing these proposed aims we will be able to achieve the design specifications and Good Laboratory Practice (GLP) animal studies that are required for FDA 510(k) device application submission.