Systems and methods for treating excess pressure having an elastic membrane in fluid contact with bodily fluid

Systems and methods are provided for treating diseases that produce elevated pressure, e.g., intraocular pressure or cerebrospinal fluid pressure, such as glaucoma or hydrocephalus, wherein the device includes a housing shell, an elastic membrane, and a local constriction that reduces the area of the fluidic passageway through the housing shell and increases fluidic resistance of the flow of fluid through the passageway. At normal IOP levels, the elastic membrane engages the local constriction to prevent or reduce fluid flow across the passageway. When the average pressure between the inlet and outlet of the device varies, e.g., exceeds a predetermined threshold, the elastic membrane deforms and disengages the local constriction to thereby permit fluid flow across the passageway.