Thirty-two patients had cardiac ventriculographic study for demonstration of the presence and degree or absence of mitral regurgitation. Four patients showed no atrial opacification, and at surgery these four were proved to have pure mitral stenosis without any mitral regurgitation. Surgical treatment of mitral stenosis demands an effective procedure for the preoperative assessment of the presence and degree or absence of mitral regurgitation. Any degree of regurgitant opacification of the left atrium during cardiac ventriculographic study is considered significant of mitral valvular insufficiency. Cardiac ventriculography does not lend itself to exactitude of interpretation but rather to estimation only of the amount of regurgitant opaque substance issuing through the mitral valve and the quantitation of mitral insufficiency. It also appears to be a reasonably efficient procedure for evaluating the effectiveness of surgical procedures designed for the correction of mitral insufficiency.