SUMMARY Left ventricular (LV) performance at rest and during multilevel exercise in the supine and upright positions was studied in seven normal subjects with equilibrium radionuclide ventriculography. The mean left ventricular end-diastolic volume (LVEDV) during supine rest was 107 4 10 ml (± SEM) and 85 ± 6 ml (p < 0.02) in the upright position; the mean resting left ventricular end-systolic volumes (LVESV) were not diSferent in the upright and supine positions. The Changes in posture at rest are associated with significant changes in LV filling and stroke volume. A transition from the supine to the upright position produces a decrease in LV end-diastolic pressure1-3 and volume4-6 and in stroke volume.' -4 6-10 The results of previous studies of the alterations in LV enddiastolic volume during exercise in the supine position have varied.5, 6, 11-15 There is general agreement that end-systolic volume is smaller during exercise than at rest;6 11, 12, 14,15 most investigators3' 6, 12, 13 have reported an exercise-induced increase in stroke volume, although others have not.1 4These data are generally consistent with an enhanced contractile state From the Departments of Medicine

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