DURING THE last decade there has been increasing interest among professional circles in cardiac surgery. A frequently used procedure has been mitral commissurotomy to open the calcified mitral valve leading to the heart.1,2There have been speculations but few objective studies on psychological sequelae of the disturbed cerebral circulation which occurs in this operation.3-6One study has stated that there is "something inherent in the surgery of mitral stenosis," perhaps the necessary occlusion of the mitral opening at intervals during commissurotomy that produces "depression of some of the psychometric scores" obtained in tests on such patients, indicating "postoperative central nervous system damage."5Reported here is an investigation of pre- and postoperative psychological test results of patients undergoing mitral commissurotomy. Method Subjects.— Two groups of eight adult male inpatients (16 in all) were selected at random from each of the two most serious classes, III and IV, of