An enhanced flexibility catheter shaft having an elongate flexible body with a proximal end, a distal end, and at least one lumen extending therethrough. A distal, flexible section on the body has a ribbed or corrugated tubular membrane having at least a first reinforcement structure, such as a first helical support, on a radially exterior or interior surface of the membrane and optionally a second reinforcement structure, such as a second helical support, on the other of the radially interior or exterior surface of the membrane
