The invention relates to an implantable access device for accessing the vascular system of a human or animal body, particularly subcutaneously implantable access port, comprising: at least one inlet opening, at least one outlet opening and at least one passageway between the at least one inlet opening and the at least one outlet opening, further comprising at least one valve assembly in the at least one passageway, which in a first, unactuated operating condition prevents a fluid flow through the at least one passageway and in a second, actuated operating condition permits a fluid flow through the at least one passageway, which is characterized in that the at least one valve assembly in the first, unactuated operating condition is longitudinally elongated and radially compressed in such a way to prevent a fluid flow through the at least one passageway and that the at least one valve assembly in the second, actuated operating condition is longitudinally compressed and radially elongated in such a way to permit a fluid flow through the at least one passageway.