A transcatheter valve prosthesis includes a self-expanding tubular stent component and a prosthetic valve disposed within and secured to the stent component. The tubular stent component has a proximal portion, a distal portion, and an intermediate portion between the proximal and distal portions. In a compressed delivery configuration, the tubular stent component has a generally circular cross-section along its length. In an expanded deployed configuration, the proximal and distal portions have a generally circular cross-section while the intermediate portion of the stent component has a generally triangular cross-section with three vertexes that are configured to project into three commissural points of a native valve when the valve prosthesis is implanted in situ. The generally triangular transverse cross-section of the valve prosthesis is formed by pulling or extending selected or particular struts of the stent component radially outwards and then applying heat to heat-set the stent component in the deployed configuration.