Since recognition of factors which modify the duration of ejection in aortic stenosis is of clinical importance, the relations among rate-corrected left ventricular ejection time, aortic valve area, and determinants of ventricular performance were studied in 54 catheterised patients. In patients with a normal cardiac index, increasing duration of ejection was linearly related to increasing obstruction. In patients with failing ventricles, on the other hand, the ejection time was less prolonged, and the duration of ejection was unrelated to valve area. At fixed valve area, relation with cardiac output, stroke volume, heart rate, mean aortic valve pressure gradient, mean aortic pressure, and left ventricular end-diastolic pressure could not adequately explain the observed scatter in ejection time. This suggests a multifactorial basis for the wide range of ejection times observed with severe aortic stenosis.