A similar procedure has been used in severely stenotic aortic valves by either advancing the balloon through the mitral valve into the aortic position or approaching the valve retrograde. Aortic balloon valvuloplasty has thus far been employed largely in severely ill, elderly patients who are judged not able to tolerate valve replacement. As noted above, results have been quite promising; low mortality and morbidity, substantial hemodynamic improvement and short hospital stays have been observed. These anecdotal reports have led to the application of balloon valvuloplasty in increasing numbers of patients. Major issues needed to be addressed prior to general acceptance of this therapy for both aortic and mitral stenosis and for operative and nonoperative candidates. The issues include: definition of risk of mortality and morbidity overall and in subgroups defined by baseline characteristics; success rate defined clinically and hemodynamically overall and in subgroups; the durability of this procedure, that is, how long will a given improvement in clinical and hemodynamic measures persist; definition of subgroups with particularly favorable or unfavorable outcomes. These questions were addressed by the NHLBI Balloon Valvuloplasty Registry.