To the Editor: Zile et al. (May 6 issue) 1 conclude that heart failure develops in patients with a normal ejection fraction because of abnormal active and passive diastolic function. However, the applicability of this conclusion to all such patients is uncertain for several reasons. First, accurate assessment of left ventricular volume, on which the conclusions critically depend, requires a three-dimensional imaging technique that measures the long axis 2 , 3 ; two-dimensional techniques are inadequate for this purpose. Second, the majority of the patients studied were men, and on average, they were less than 60 years of age. However, most patients with . . .