Recent studies suggest that the partial ejection fraction (EF) in early systole is a more sensitive index of left ventricular (LV) dysfunction than the holosystolic EF. We examined LV volume, partial EF, and volume increment at each of 12 time points in systole to determine which parameter best distinguishes normal subjects from patients with coronary artery disease (CAD). Contrast ventriculograms, obtained either in the right anterior oblique projection (60 frames/sec) or in the biplane projection (30 frames/sec), of 58 normal subjects and 68 patients with CAD were studied. The endocardial contour in each frame of a sinus beat was traced to derive a volume curve. At each twelfth of systole, LV volume was extrapolated from the curve and the partial EF was calculated. The increment in volume between successive time points was also calculated. Both partial EF and LV volume in patients with CAD became progressively more abnormal with time; peak abnormality occurred at end-systole. In a subgroup of patients with CAD who had normal holosystolic EF, both partial EF and volume were normal throughout systole. The increment in volume with each twelfth of systole in patients with CAD deviated less than 1 SD from normal throughout systole. Thus, maximum abnormality in partial EF and volume occurs at end-systole. Of the parameters of global LV function tested, holosystolic EF best distinguishes patients with CAD from normal subjects. However, regional wall motion measured in the area of interest is more sensitive to localized abnormality, the severity of which may be overestimated or underestimated by the EF due to hyperkinesis or hypokinesis in other regions of the left ventricle. Circulation 68, No. 4, 756-762, 1983. CORONARY ARTERY STENOSIS is associated with hypokinesis and reduced global function.' Early studies compared the extent of motion at end-systole with the left ventricular (LV) dimensions at end-diastole.24 These studies have been extenided to include measurement of LV function at time points within systole.7-9 Recently some investigators have reported an abnormality in regional wall motion and ejection fraction (EF) in early systole in patients with normal holosystolic function,IO'3 suggesting that indices of function measured early in systole may be more sensitive to LV dysfunction than indices measured at end-systole. This has been of interest because patients may have a normal holosystolic EF despite significant coronary stenosis or previous myocardial infarction. Other investigators, however, have been unable to confirm this finding.'0' 14-16 Furthermore, the studies showing subnormal EF in early systole examined only one or two points in time. The present study was conducted to determine the time in systole at which global LV function exhibits maximum abnormality and the parameter that is most sensitive for the LV dysfunction in coronary artery disease. Therefore, volume, increment in volume, and partial EF at each twelfth of systole were measured and compared between normal subjects and pati...