Atrial pacing was performed in 10 patients with various degrees of aortic valvular stenosis (AVS) and the hemodynamics were compared to eight normal subjects. Similar maximum heart rates (135 ± 6/min) in each group resulted in no significant complications or symptoms and no changes in cardiac output or transvalvular pressure difference while stroke work (SW) and volume and left ventricular end-diastolic pressure (LVEDP) declined. A postpacing overshoot in LVEDP (control, 14 ± 2; postpacing, 25 ± 3 mm Hg;p= 0.01) which occurred in the cases of AVS probably reflects a decrease in myocardial compliance. Pacing ventricular function curves relating induced changes in SW and LVEDP were generally steeper in patients with AVS than in the normal subjects and were definitely abnormal in three of the former. Pulsus alternans induced in two patients was associated with abnormal myocardial function while the control LVEDP level was not a good indication of the functional response of the myocardium.Atrial pacing appears to be beneficial in the preoperative evaluation of the patient with AVS when exercise stress may be dangerous because of the possibilities of inducing arrhythmias, syncope, and sudden death. It permits precisely controlled evaluation for preoperative and postoperative comparison.