A commissurotomy catheter and method for separating fused heart valve leaflets using the catheter is disclosed. The catheter is comprised of a lumen having at least two inflatable balloons at its operational end and at least one cutting edge between the balloons. To separate the fused leaflets the catheter is positioned within the heart so that it extends through the fused leaflets with a balloon on either side of the leaflets. Then the balloons are inflated which forces the cutting edge against the fissure between the fused leaflets and separates them. After separation the balloons are deflated and the catheter is removed.