Abstract: A balloon dilatation catheter is provided which has a stiff proximal cannula made of a material such as metal hypotubing. The distal end of the catheter includes an inflatable medical device balloon, an inflation lumen and a guidewire lumen. A coiled transition assembly is positioned between the proximal cannula and the distal end section. This coiled transition assembly has a tightly wound coil within a tube and provides for a flexible transition between the two components of diverse stiffness, namely the proximal cannula and the flexible distal end portion. The dilatation catheter typically has an easily or rapidly exchangeable feature and is used in conjunction with a guiding catheter. During a procedure when the catheters are within the vascular system, the coiled transition section of the dilatation catheter readily follows tightly curved portions of the inserted guiding catheterby.