This invention is a method, a device for introduction of a catheter (6C), and/or delivering a fluid, such as oxygenated blood, to a patient's vascular system including a cannula (2C) having an expandable portion (4C). The expandable portion (4C) is movable from a collapsed position to an expanded position. The expandable portion (4C) is inserted into the patient in the collapsed position which facilitates introduction and advancement of the cannula (2C) through the patient's blood vessel. After introduction into the patient, the expandable portion (4C) is moved to the expanded position. The expandable portion (4C) protects the blood vessel against fluid forces when flowing a fluid through the cannula (2C), and protects the vessel from contact with the catheter (6C) advanced through the cannula (2C).