Embodiments relate to delivery systems for accessing a blood vessel. The delivery systems include a shaped accessory sheath having a default shape that may be temporarily altered to facilitate insertion through a patient's blood vessel and returned to the default shape after insertion to facilitate a medical procedure. Some of the present accessory sheaths are configured to have their default shapes altered via a dilator having a stiffness greater than that of a corresponding portion of the accessory sheath. Others of the present accessory sheaths are configured to have their respective default shapes altered by a shape memory material (SMM) that alters shape responsive to changes in certain condition(s) such as temperature.
