Changes in the physiologic state of the patient may affect indices of valvular aortic stenosis. We determined the effects of supine exercise on the Gorlin valve area, Cannon valve area, aortic valve resistance, and a modified stroke work loss index in 80 patients with aortic stenosis. Exercise caused a significant increase in the Gorlin and Cannon valve area, while work loss and valve resistance decreased significantly. The average percent change in work loss, 12.2%, was lower than the other indices (P less than 0.02), i.e., 15.3% for valve resistance, 18.6% for the Gorlin area, and 19.3% for the Cannon area. The correlation between the rest and exercise measurements was highest for work loss (r = 0.94), compared to 0.93, 0.88, and 0.89 for the other 3 indices, respectively. In patients with a Gorlin area below 1 cm2, exercise caused a significant decrease in work loss, but not Cannon area or valve resistance. However, the percent change was significantly lower and the correlation was better with the work loss index. We conclude that the work loss index is less affected by supine exercise than other indices of aortic stenosis.