A catheter comprising a dual lumen tube with a bolus at its distal end having a bullet nose. A venous port is formed in one side of the bolus adjacent the bullet nose of the bolus. An arterial port is formed in the bolus circumferentially displaced 180° around the catheter from the venous port. The bolus contains a venous passage which transitions from a smaller two-thirds moon shaped cross-section to a larger circular cross-section. The arterial passage has a crescent-moon shaped cross-section. The bullet nose is not as thick as the tube and is inclined on an angle to the axis of the tube so that a portion of its outer periphery is substantially tangent to a hypothetical cylinder containing the trailing edge of the venous port.