An I.V. flush syringe assembly includes a barrel having an inside surface defining a chamber for retaining fluid, an open proximal end and a distal end with a passageway therethrough in fluid communication with the chamber. An elongate plunger having a proximal end, a distal end and a stopper is slidably positioned in fluid-tight engagement with the inside surface of the barrel.for drawing fluid into and out of the chamber by movement of the stopper relative to the barrel. The plunger includes anti-reflux structure for minimizing stopper deflection when fluid has been delivered from the chamber and the stopper is being forced against the distal end of the chamber.
