Current guidelines postulate that “Severe aortic stenosis is unlikely if cardiac output is normal, and there is a mean pressure gradient < 50 mmHg”. However, there is a large group of patients with apparently preserved left ventricular pump function in whom the severity of aortic stenosis appears to be severe judged by their valve orifice area, but moderate (or even mild) by their transvalvular gradients. The existence of this entity is still not widely accepted, since relativley low gradients are deemed unlikely in the presence of both severe aortic stenosis and preserved ejection fraction. However, recent research has demonstrated that in these patients, concentric left ventricular hypertrophy, low left ventricular volumes, increased systemic vascular resistance in the presence of arterial hypertension, and masked left ventricular dysfunction - in spite of preserved or mildly impaired ejection fraction - lead to small stroke volumes and consequently to low gradients. Nevertheless, these patients do have severe aortic stenosis, and their prognosis is markedly impaired, in particular, because they are often deemed uneligible for aortic valve replacement due to their unimpressive transvalvular gradients.  The existing data suggest that the cut-off values for severity should be adjusted to incorporate this constellation by allowing for relatively low gradients as long as aortic valve area - after careful evaluation mindful of potential errors - is confirmed to be < 1 cm2.