Balloon dilatation catheter adapted to be utilized in connection with a guiding catheter and a guide wire. The catheter comprises a flexible elongate tubular member having proximal and distal extremities and having a lumen extending therethrough. An inflatable balloon is mounted on the distal extremity of the tubular member. The interior of the inflatable balloon is in communication with the lumen. A sleeve extends through the balloon and extends rearwardly from the balloon and alongside the lumen. The sleeve has a guidewire lumen extending therethrough. The guidewire lumen is adapted to receive a guide wire extending therethrough and extending rearwardly of the flexible elongate element into a region adjacent the proximal extremity of the proximal elongate element. The sleeve has a slit extending longitudinally of the same from the proximal extremity of the sleeve to a region adjacent the balloon permitting the guide wire to be removed therethrough.