['Left ventricular (LV) stroke work loss (SWL) is an index of aortic stenosis (AS) severity based on the energy loss concept. Traditionally known as an invasive measurement, SWL has also been determined noninvasively using Doppler echocardiography. The present work was done to compare the echocardiographic estimate against the standard invasive SWL.', 'We determined SWL in 113 adult patients with AS at cardiac catheterization (mean gradient as percentage of the LV mean systolic pressure) and by Doppler echocardiography (mean gradient as percentage of the sum of systolic cuff blood pressure and mean gradient). SWL averaged 26.5+/-0.6% by echocardiography vs 30.9+/-0.8% by catheterization (p<0.0000001). The underestimation by echocardiography was the worse the higher the invasive SWL was (p<0.00001). Echocardiographic SWL exceeding 25% (previously suggested cutoff) had a sensitivity of 64% and specificity of 74% to identify severe AS (Gorlin valve area<0.5 cm(2)/m(2)). Several patients with severe AS by valve area had echocardiographic SWL suggesting only mild AS.'] Does doppler echocardiography markedly underestimate left ventricular stroke work loss in severe aortic valve stenosis?