Vascular catheters, for use in rats, have stood the test of time because they are affordable and they work! These catheters, modified from the original design of Tinsley (1983), are fabricated from Braintree Scientific's medical grade polyethylene (PE) tubing and Braintree Scientific's silicone tubing (RenaSil) and sealed with a stainless steel plug. When filled with a viscous catheter lock solution they maintain a very high rate of patency* for several weeks. *Patency, especially for blood sampling, is highly dependent on the location of the intravascular tip. Both the thoracic and femoral rat models have the following features: Externalized polyethylene (PE) tubing catheter port: Flared for easy access with a blunted 23g hypodermic needle for sampling or infusion. Port is sealed with 0.025 " diameter stainless steel plug when not in use. Catheter port is designed to exit between the scapulae and to be secured with a single Autoclip 9 mm stainless steel wound clip. Polyethylene (PE) tubing catheter body: The rigidity of polyethylene (PE) tubing minimizes the incidence of catheter lumen constriction and relaxation, an "eye dropper" effect, which allows blood to enter the intravascular tip. All catheter anchor points allow for suturing around the polyethylene (PE) tubing minimizing the likelihood of suture induced catheter lumen constriction. RenaSil intravascular tip: RenaSil as the intravascular tip for reducing intravascular thrombus formation. Reduced diameter intravascular tip: Reducing the inner diameter of the intravascular tip relative to the inner diameter of the port allows for efficient expulsion of blood from the intravascular tip. The last step following catheter implantation or use should be to advance the stainless steel plug into the port for a few millimeters. This is sufficient to expel trace amounts of blood from the intravascular tip with a minimum amount of catheter lock solution entering the bloodstream.