Inflatable and deflatable balloon catheters are disclosed. Catheters according to the invention have an expansion chamber that may be elongated to reduce its radial dimension without producing oblique or transverse folds or wrinkles. The inflatable chamber of the catheter is supported by an elongated support member of small diameter which has a continuously extending opening therein through which fluid is admitted to and withdrawn from the chanber. An axially movable elongating member is disposed within the expansion chamber for elongating the chamber. Axial movement of the elongating member elongates the chamber to decrease its radial dimension whereby feeding and guiding of the catheter is facilitated. In one embodiment, the support member is the gas supply tube extending into the chamber and the continuously extending opening is a helical slit running along at least part of the tube enclosed by the chamber. In another embodiment, the support member is a helical spring secured within the chamber to one end of the gas supply tube and the continuously extending opening is the space between coils of the spring. Also, in the disclosed embodiments, the catheter is an intra-aortic balloon catheter. A method is also disclosed for fabricating and using catheters according to the invention.