Devices and methods for assisting valve function, replacing venous valves, and predicting valve treatment successes. In at least one embodiment of an endograft valve device of the present disclosure, the device comprises an endograft body configured for expansion from a collapsed configuration to an expanded configuration within a luminal organ and comprising a first portion having a proximal end defining a proximal end aperture and a distal end defining a distal end aperture, the first portion tapering toward the distal end so that the distal end aperture has a relatively smaller cross-sectional area than the proximal end aperture when the valve device is expanded, and a valve portion positioned at or near the distal end of the first portion, the valve portion configured to receive fluid flowing through the distal end aperture of the first portion.
