commissurotomy

noun

com·​mis·​sur·​ot·​o·​my ˌkäm-ə-ˌshu̇(ə)r-ˈät-ə-mē, -shə-ˈrät- 

plural commissurotomies

: the operation of cutting through a band of muscle or nerve fibers

specifically : separation of the flaps of a mitral valve to relieve mitral stenosis : valvulotomy