Abstract: An injection shut-off valve for insertion into an infusion line comprises a housing with connections for inlet and outlet lines. The housing includes an orifice for introducing an injection syringe. A valve is installed in the housing and includes a deformable diaphragm. In a non-injection state, the valve device seals off fluid flow between the inlet and outlet lines on the one hand and the orifice on the other. During injection, the diaphragm is deformed to create an opening such that fluid flow from the inlet to the housing is shut off. During deformation of the diaphragm the orifice is brought into fluid carrying communication with the outlet line from the housing, thus making it possible for the injection fluid to pass through the housing into the outlet line, and to a patient.