A catheter for introducing material into the vascular system is provided. The catheter includes an elongated catheter body having a side wall defining a catheter lumen. The catheter body has a proximal portion. Material can be introduced into the catheter lumen at its proximal portion. The catheter body has a distal portion. The distal portion has a single wall in an exit zone. At least one pressure responsive exit is formed in the side wall of the distal portion of the catheter body. The pressure responsive exit permits material to exit from the catheter lumen in response to a pressure over a first pre-determined amount while preventing material from entering into the catheter lumen at a pressure less than a second pre-determined amount.