Surgeons use a procedure called valvotomy to separate fused leaflets in the valve.    From Wordnik.com.  [Pulmonary Stenosis] Reference

(November 20, 2000) - For patients with rheumatic mitral stenosis, balloon mitral valvotomy yields similar long-term results compared to a surgical procedure called commissurotomy, according to a University of Pittsburgh.    From Wordnik.com. Reference