The invention relates to a blood treatment cassette (1000), comprising a cassette body designed as a hard part (1) and comprising a film (3), wherein the film (3) is connected to the hard part (1) and covers the hard part (1) at least in some sections, wherein the hard part (1) has at least one valve seat or valve section or a valve base (226) for a valve (288), wherein the valve (288) is designed to assume, in addition to a first, open position of the valve (288), in which the valve base (226) and a section of the film (3) arranged above the valve base do not touch each other, a second, closed position of the valve (288) when a force is applied to the section of the film (3), in which second position of the valve the valve base (226) and the section of the film (3) touch each other, wherein the blood treatment cassette (1000) has at least one spacer resiliently or elastically supported on the hard part (1) or produced integrally with the hard part, wherein the spacer is arranged in order to apply stress, force, or pressure to the section of the film (3) arranged above the valve base (226) in the first position.
