An ultrasound system for planning a surgical implantation of a prosthetic aortic valve produces three dimensional images of the aortic root region of a patient. An electronic model of an aortic root is accessed and fitted to the aortic root in a three dimensional ultrasound image. Preferably the aortic root model exhibits closed contour cross-sections which are fitted to the endothelial lining of the aortic root in the ultrasound image. A medial axis of the fitted model is identified and radii measured from the medical axis to the border of the fitted model. The radii are joined to identify a surface forming a mesh model fitted to the aortic root anatomy of the patient. The shape and dimensions of the fitted model may be used to fabricate a custom prosthetic valve for aortic valve replacement.