Perfusion-type balloon dilatation apparatus having a guiding catheter with proximal and distal extremities and with a flow passage extending therethrough. A balloon dilatation catheter is disposed in the guiding catheter. The balloon dilatation catheter is comprised of a flexible elongate tubular member having proximal and distal extremities and having a first lumen extending therethrough. First and second inflatable balloons are carried by the tubular member and having their interiors in communication with the first lumen in the tubular member. The first balloon is positioned within the guiding catheter. The second balloon is positioned adjacent the distal extremity of the tubular member. A second lumen is carried by the tubular member and extends through the first and second balloons and through the distal extremity of the tubular member. The second lumen has an opening proximal of the first balloon and opens into the interior of the guiding catheter. An adapter is carried by the proximal extremity of the guiding catheter and provides a liquid-tight seal between the guiding catheter and the dilatation catheter and also provides an inlet through which liquid can be introduced so that it can travel through the flow passage in the guiding catheter and into the second lumen carried by the dilatation catheter so that the liquid can flow through the second lumen beyond the second inflatable balloon.