The disclosure relates to heart valve prostheses with the reduced need of pacemaker implantation and improved means for positioning the replacement heart valve. In one aspect of the present disclosure, the stent scaffold of the valve prosthesis includes axially extending locators. The locators may be positioned within the cusp of the native aortic valve. Placement of the locators within the cusps may prevent further proximal movement of the stent scaffold into the left ventricle. By adjusting the location of the proximal end of the locators with respect to the proximal end of the stent scaffold, infra-annular placement of the stent scaffold in the aortic annulus may be assured. In another aspect, means for visualizing the positioning of replacement heart valves at an implant site inside an individual's body is disclosed.