SURGICAL attempts to enlarge the orifice of the mitral valve, previously constricted by disease, were consistent failures until the principle of cutting or splitting the scarred valve ring at the commissures was recognized by Bailey in 1946. At that time Bailey performed a digital dilatation of the valve in a severely ill patient and obtained a marked temporary improvement. He recognized at autopsy that the valve enlargement which had resulted from the dilatation was due to tearing directly at the location of the commissures. He and his group have since developed more accurate methods of commissurotomy to accomplish this result.1
Previously, in 1925, Souttar2 had accidentally produced a commissurotomy during digital dilatation of the mitral valve. He did not, however, realize what fundamental principle was involved.
In 1948 Harken, Ellis, Ware, and Norman3 described their experiences with a procedure in which they removed a segment of the