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Objective: : The principal limitations of percutaneous techniques to replace the aortic valve are detailed visualization and durable prostheses. We report the feasibility of using real-time magnetic resonance imaging (MRI) to provide precise anatomic detail and visual feedback to implant a proven bioprosthesis., Methods: : Twelve domestic pigs were anesthetized, and, through a minimally invasive approach using real-time MRI guidance, underwent aortic valve replacement. This was accomplished on the beating heart by using a commercially available bioprosthesis. MRI was used to precisely identify the anatomic landmarks of the aortic annulus, coronary artery ostia, and the mitral valve leaflets. Additional intraoperative perfusion, flow velocity, and functional imaging were used to confirm adequacy of placement and function of the valve., Results: : Under real-time MRI, multiple oblique planes were prescribed to delineate the anatomy of the native aortic valve and left ventricular outflow track. Enhanced by the use of an active marker wire, this imaging allowed correct placement and orientation of the valve. Through a transapical approach, a series of bioprosthetic aortic valves (21 to 25 mm) were inserted. The time to implantation after the placement of the trocar to deployment of the valve was less than 90 seconds. The average procedure duration was less than 40 minutes, Conclusions: : Real-time MRI provides excellent anatomic detail and intraoperative assessment that permits placement of durable valve prostheses on the beating heart without the limitations of percutaneous approaches.