Valvular stenosis or incompetence results in an estimated 41,000 valve replacements in the United States each year. These replacements are equally distributed between the aortic and mitral valves. An estimated 60 percent of aortic valve replacements are the result of valve stenosis; 20-30 percent of mitral valve replacements are due to stenosis. The risk of operative mortality in single valve replacement ranges from 3 percent to as high as 15 percent depending upon patient characteristics. Morbidity associated with open heart procedures includes wound infection, reoperation for bleeding, and post-operative pain. Most patients with artificial valves require anticoagulant therapy for the rest of their lives and thus face the competing risks of hemorrhage and valve thrombosis/embolism. In addition, there are a number of patients with aortic stenosis who are not candidates for aortic valve replacement because of unacceptable operative risks who might be dramatically improved by balloon valvuloplasty.