An artificial valve (5; 10; 20; 30; 50) for implantation in a mammal body, comprising: a casing (12; 37; 61); and a closing mechanism; wherein the closing mechanism comprises a first moving part (11; 21, 22; 31, 32, 33; 51) adapted to move relative to the casing (12; 37; 61) to assume an open position and a closed position for opening and closing, respectively, a blood flow through a blood vessel of the body, as well as positions between said open and closed positions; wherein the closing mechanism (11; 21, 22; 31, 32, 33; 51) is adapted to control movement of the first moving part and to allow the first moving part to move in response to a physical parameter of the mammal, or a functional parameter of a device used by the mammal, reaching a predetermined threshold value, the physical or functional parameter being one or more of the following: the blood pressure on at least one side of the artificial valve or the difference in blood pressure between an inner and an outer side of the artificial valve in its closed position, the blood flow at a defined point in the circulatory system of the mammal, a physical parameter related to the contraction of a muscle of the mammal, a body generated parameter related to the contraction of the mammal's heart muscle, and a device generated signal related to the contraction of the mammal's heart muscle; characterised in that the closing mechanism is adapted to: - in a closed position of the first moving part, allow the first moving part to move freely in a passive opening movement, and - in a position of the first moving part between the open and closed positions, control the movement of the first moving part, thus not allowing passive movements. a casing (12; 37; 61); and a closing mechanism; wherein the closing mechanism comprises a first moving part (11; 21, 22; 31, 32, 33; 51) adapted to move relative to the casing (12; 37; 61) to assume an open position and a closed position for opening and closing, respectively, a blood flow through a blood vessel of the body, as well as positions between said open and closed positions; wherein the closing mechanism (11; 21, 22; 31, 32, 33; 51) is adapted to control movement of the first moving part and to allow the first moving part to move in response to a physical parameter of the mammal, or a functional parameter of a device used by the mammal, reaching a predetermined threshold value, the physical or functional parameter being one or more of the following: the blood pressure on at least one side of the artificial valve or the difference in blood pressure between an inner and an outer side of the artificial valve in its closed position, the blood flow at a defined point in the circulatory system of the mammal, a physical parameter related to the contraction of a muscle of the mammal, a body generated parameter related to the contraction of the mammal's heart muscle, and a device generated signal related to the contraction of the mammal's heart muscle; the blood pressure on at least one side of the artificial valve or the difference in blood pressure between an inner and an outer side of the artificial valve in its closed position, the blood flow at a defined point in the circulatory system of the mammal, a physical parameter related to the contraction of a muscle of the mammal, a body generated parameter related to the contraction of the mammal's heart muscle, and a device generated signal related to the contraction of the mammal's heart muscle; characterised in that the closing mechanism is adapted to: - in a closed position of the first moving part, allow the first moving part to move freely in a passive opening movement, and - in a position of the first moving part between the open and closed positions, control the movement of the first moving part, thus not allowing passive movements. - in a closed position of the first moving part, allow the first moving part to move freely in a passive opening movement, and - in a position of the first moving part between the open and closed positions, control the movement of the first moving part, thus not allowing passive movements.