Abstract: A hose or tubular guide catheter which accommodates and guides a balloon catheter through a portion of the vascular system to a site where the balloon catheter can be employed for the dilatation of coronary arteries. The wall of the catheter, in the region of its anterior end, is set back from the edge over a portion of the circumference. If the end of this guide catheter has passed only a little way into the entrance of a coronary artery, blood from the aorta can enter through the large flow section into the catheter and into the coronary artery. Hence the blood supply of the coronary artery is assured. By further advance of the guide catheter, the recess is closed off by the wall of the entrance opening of the coronary artery, so that injected contrast medium will enter full into the coronary artery and cannot pass into the aorta.