The assembly includes two or more tubes T1, T3 fused together to form a single tube shaft, at least one of the tubes being formed of a pressure resistant material. The tubes are fused by a heat shrinkable tube slide placed over a segment of catheter tubes while metallic mandrels M1, M2 are passed through each tube lumen to protect the lumens during fusion. The heat shrinkable tube will shrink and apply the required pressure over the catheter tubes. Continual heating will melt and re-shape the catheter tubes inside the heat shrinkable tube while the latter will not be affected due to its high melting temperature. After cooling, the heat shrinkable tube is removed and the metallic mandrels are pulled back. One or more of the tubes can be of different hardness, material and/or color. The difference will provide pressure resistant lumens, overall catheter elasticity and/or identification. The distal end of the united catheter tube can be split, free floating, stepped, tapered tipped or have side openings (fig 5). The proximal segment (non-fused) may form catheter extension legs.
