An anti-reflux catheter comprising: - A support center body having an inner longitudinal passage chamber, briefly inner chamber; - A cannula prolonging from one end of the center body and connected to the inner chamber; - A transversal opening crossing the center body and communicating with the inner chamber; - A prolonging extension of the transversal opening toward the outside; - A flexible sleeve longitudinally and coaxially fitted in the inner chamber in correspondence with the transversal opening and having an outer surface facing said transversal opening; - pressing means (10, 11) acting on said sleeve and movable between a deactivated position or an activated position, and vice versa, associated with said transversal opening, said pressing means (10, 11) being activated from the outside, said pressing means comprising: - A maneuvering member slidingly coupled to said extension and to be alternatively positioned between a deactivated position raised from said center body or an activated position lowered toward said center body; - A shutter actuated by said maneuvering member and slidingly received in a sliding chamber defined inside said extension, said shutter having an active contact end with the outer surface of said sleeve and an oppposing end connected to said maneuvering member (10 said maneuvering member being a plug fitted on said extension, the anti-reflux catheter further comprising guide means (20, 21) provided for the plug and the extension, said guide means being capable to guide the plug between a deactivated position and an activated position, said guide means comprising at least a coupling between a concave member and a convex member engaging said concave member; said concave element comprising at least a groove obtained in the outer surface of said extension and said convex element comprises at least a pawl extending from an inner surface of said plug, characterized in that said groove is a helical groove wherein: temporary retention means are provided for the helical groove and the plug, said temporary retention means being capable to retain the plug in the activated position; and wherein said temporary retention means comprise: - At least one end segment of said helical groove; the pawl projecting from said plug and removably engageable in said end segment when said plug is in said activated position, said end segment being counter-sloped with respect of said helical groove. - A support center body having an inner longitudinal passage chamber, briefly inner chamber; - A cannula prolonging from one end of the center body and connected to the inner chamber; - A transversal opening crossing the center body and communicating with the inner chamber; - A prolonging extension of the transversal opening toward the outside; - A flexible sleeve longitudinally and coaxially fitted in the inner chamber in correspondence with the transversal opening and having an outer surface facing said transversal opening; - pressing means (10, 11) acting on said sleeve and movable between a deactivated position or an activated position, and vice versa, associated with said transversal opening, said pressing means (10, 11) being activated from the outside, - A maneuvering member slidingly coupled to said extension and to be alternatively positioned between a deactivated position raised from said center body or an activated position lowered toward said center body; - A shutter actuated by said maneuvering member and slidingly received in a sliding chamber defined inside said extension, said shutter having an active contact end with the outer surface of said sleeve and an oppposing end connected to said maneuvering member (10 said maneuvering member being a plug fitted on said extension, the anti-reflux catheter further comprising guide means (20, 21) provided for the plug and the extension, said guide means being capable to guide the plug between a deactivated position and an activated position, said guide means comprising at least a coupling between a concave member and a convex member engaging said concave member; said concave element comprising at least a groove obtained in the outer surface of said extension and said convex element comprises at least a pawl extending from an inner surface of said plug, characterized in that said groove is a helical groove wherein: temporary retention means are provided for the helical groove and the plug, said temporary retention means being capable to retain the plug in the activated position; and wherein said temporary retention means comprise: - At least one end segment of said helical groove; the pawl projecting from said plug and removably engageable in said end segment when said plug is in said activated position, said end segment being counter-sloped with respect of said helical groove.