Problems with the use of the diagnostic angiography catheter as a therapeutic tool relate to difficulty in placing the catheter precisely in the desired area and controlling the infusion of the occluding agent. A soft microcatheter was developed to overcome these problems. The catheter ends in a balloon tip and can be flow-directed. To overcome the traditional difficulties of flow-guided catheters and the need for a double lumen, a calibrated leak in the balloon allows distal fluid delivery while the balloon remains inflated.