A prosthetic tri-leaflet valve formed by involuting a portion of a tubular structure inside itself. The valve can be made by a method comprising providing a tubular segment in which three equidistant longitudinal incisions are made in one end of the tube creating three flaps which are involuted, i.e., folded, in toward the inside of the tube and the edges of the flaps secured to the inner wall of the tube to form leaflets. The tube can be formed of a single sheet of synthetic, organic or biological material and can be solid, woven, braided or the like. A braided configuration permits the valve to be annularly compressed and delivered to the site using a minimally invasive delivery mechanism, then expanded at the implantation site.