Some divergence of opinion exists as to the merits of “closed” versus “open” commissurotomy for the correction of pure acquired mitral stenosis (9). Part of this controversy is probably due to the small but real percentage of early failures, as well as to the relatively frequent recurrence of mitral stenosis following the procedure (6). Such recurrences and failures may be due in part to the presence of one of the following pathologic features of the mitral valve: insufficient closure; heavy calcification; significant reduction in functioning valve tissue with scarring and fusion; extensive deformities of the valve secondary to abnormalities of the chordae tendineae. Also, thrombi in the left atrium, with their possible dislodgment at surgery, may present formidable technical problems for the surgeon. The assessment of the functional derangement of the mitral valve is best achieved by selective angiocardiography, in conjunction with and complementary to hemodynamic evaluations of cardiac function by simultaneous right and left heart catheterizations. If it can be established that available valve tissue with good mobility is adequate, regardless of the severity of stenosis, and that calcium or thrombus are absent, then “closed” commissurotomy is the treatment of choice at this medical center (Strong Memorial Hospital, Rochester, N. Y.). It is the purpose of this paper to present specific angiographic criteria for the delineation of the mitral valve leaflets, obtained by special positioning of the patient and the x-ray tube, which may assist the surgeon in his selection of the most effective and least hazardous procedure for the correction of acquired mitral stenosis. Method To visualize the mitral valve components most clearly, the patients are placed in a steep left posterior oblique position of 50 to 70 degrees. The x-ray tube is angled toward the head 15 to 20 degrees. The tip of the Brockenbrough catheter, introduced by a saphenous vein cut-down and advanced by a transseptal puncture (3) into the left atrium, should be pointed at the mitral valve orifice toward the left ventricle. The serial roentgenograms are exposed as rapidly as possible; we can obtain at least 6 frames per second. Forty ml of contrast material (sodium Hypaque diatrizoate) are injected at the minimal rate of 20 to 25 ml per second. The angiocardiograms are usually obtained during the cardiac catheterization studies. The “stenotic” valve leaflets, as described by Kjellberg and others (7, 10, 11), are visible throughout each cardiac cycle. They may be seen as a thickened, radiolucent border or band, separating the atrium from the ventricle. If an adequate amount of functioning valve tissue is present, the abnormal leaflets may balloon as a “dome” into the left ventricular cavity during ventricular diastole.