Abstract: A heart valve prosthesis includes an annular body, a support having an upstream support surface, a downstream support surface and a side surface facing the central axis of the annular body, and leaflets mounted within the annular body so as to pivot between a closed position in which the blood backflow is restricted and an open position which allows the passage of the direct blood flow. Each leaflet has a contact surface cooperating with the contact surface of the other leaflet in the closed position, an outer side surface, an upstream surface, a downstream surface and support portions respectively interacting with the downstream support surface and the upstream support surface of the support of said annular body.