An endovascular device for reducing a reflux of an embolizing agent in a vessel during an embolization therapy procedure, the device comprising: an elongated delivery catheter having a proximal end and a distal end defining an open tip, said delivery catheter capable of delivering the embolizing agent through said open tip of said distal end, a valve having a proximal end, said valve coupled at its proximal end to said distal end of said catheter such that embolizing agent delivered through said delivery catheter feeds into said proximal end of said valve, said valve having a plurality of filaments (203a, 203b, 203c) in the form of a braid, said valve configured and biased to radially expand from an undeployed state to a deployed state, wherein said valve in said undeployed state has a diameter smaller than or approximately equal to an outer diameter of said catheter, and in said deployed state has a diameter substantially larger than said outer diameter of said catheter; and wherein once said valve is in said deployed state in the vessel, said valve is dynamically movable between an expanded valve-open configuration and a collapsed valve-closed configuration depending on the local biological fluid pressure about said valve, and characterized in that: said valve further comprises a filter attached to said plurality of filaments (203a, 203b, 203c) by coating said filter onto said plurality of filaments (203a, 203b, 203c), said filter having pores of a characteristic diameter of between 10μm and 500μm, wherein when the fluid pressure is higher on a proximal side of said valve, said valve is in said valve-closed configuration permitting fluid flow about the valve, and when said pressure is higher on a distal side of said valve, said valve is in said valve-open configuration in which said valve contacts the vessel wall and said characteristic diameter of said pores of said filter renders said filter impermeable to the embolic agent such that the valve is thereby adapted to reduce reflux. an elongated delivery catheter having a proximal end and a distal end defining an open tip, said delivery catheter capable of delivering the embolizing agent through said open tip of said distal end, a valve having a proximal end, said valve coupled at its proximal end to said distal end of said catheter such that embolizing agent delivered through said delivery catheter feeds into said proximal end of said valve, said valve having a plurality of filaments (203a, 203b, 203c) in the form of a braid, said valve configured and biased to radially expand from an undeployed state to a deployed state, wherein said valve in said undeployed state has a diameter smaller than or approximately equal to an outer diameter of said catheter, and in said deployed state has a diameter substantially larger than said outer diameter of said catheter; and wherein once said valve is in said deployed state in the vessel, said valve is dynamically movable between an expanded valve-open configuration and a collapsed valve-closed configuration depending on the local biological fluid pressure about said valve, and characterized in that: said valve further comprises a filter attached to said plurality of filaments (203a, 203b, 203c) by coating said filter onto said plurality of filaments (203a, 203b, 203c), said filter having pores of a characteristic diameter of between 10μm and 500μm, wherein when the fluid pressure is higher on a proximal side of said valve, said valve is in said valve-closed configuration permitting fluid flow about the valve, and when said pressure is higher on a distal side of said valve, said valve is in said valve-open configuration in which said valve contacts the vessel wall and said characteristic diameter of said pores of said filter renders said filter impermeable to the embolic agent such that the valve is thereby adapted to reduce reflux. said valve further comprises a filter attached to said plurality of filaments (203a, 203b, 203c) by coating said filter onto said plurality of filaments (203a, 203b, 203c), said filter having pores of a characteristic diameter of between 10μm and 500μm, wherein when the fluid pressure is higher on a proximal side of said valve, said valve is in said valve-closed configuration permitting fluid flow about the valve, and when said pressure is higher on a distal side of said valve, said valve is in said valve-open configuration in which said valve contacts the vessel wall and said characteristic diameter of said pores of said filter renders said filter impermeable to the embolic agent such that the valve is thereby adapted to reduce reflux.