A foldable one-way valve prosthesis has an open state allowing a fluid to pass therethrough, and a closed state, preventing or at least reducing a reverse fluid flow therethrough. Each leaflet has an upstream edge extending between two upstream vertices and a downstream edge extending between two downstream vertices. The downstream edge has a folding point dividing the downstream edge into a long section extending between the folding point and a first of the downstream vertices, and a short section extending between the folding point and a second of the downstream vertices. Each leaflet further has a pair of side edges extending between opposite upstream and downstream vertices of the respective upstream and downstream edges； and a folding line extending between the folding point and a point on the upstream edge constituted by or disposed adjacent to the upstream vertex of the side edge, whose downstream vertex is the first downstream vertex. The leaflets are attached to each other along their common side edges with a possibility of pivoting relative to each other about the common side edge when the leaflets are folded along their folding lines causing the short section of the downstream edge to be angled with respect to the long section thereof, so as to bring the valve prosthesis into the closed state.
