Subjects with low-flow/low gradient severe aortic stenosis can be included, provided low-dose dobutamine or exercise stress echocardiography demonstrates a mean gradient of > 40 mmHg or a maximal aortic valve velocity of > 4.0 m/sec, AND aortic valve area of < 1.0 cm2 (or aortic valve area index of < 0.6 cm2/m2).