A chest-mounted left ventricular (LV) nuclear probe (VEST™) for use during arm and leg ergometry is presented, with a discussion of the validity and reproducibility of LV function measures at rest and exercise. During both arm and leg ergometry in trained subjects, transient changes in LV function/volumes were observed. LV ejection fraction and relative end-systolic and end-diastolic volumes were 25 to 30% less with the arms versus the legs, agreeing with data from other studies using conventional techniques. At peak exercise with both limbs, LV ejection fraction and relative LV end-systolic volume increased, followed by immediate postexercise normalization. The effect was greatest with the arms and reflects the effect of high intramuscular and arterial pressures generated during arm cranking, leading to increased LV afterloading. The VESTTMpermits rapid and noninvasive assessment of LV function during arm exercise, avoiding the limitations of other techniques.Key words: arm exercise, radionuclide, chest-mounted probe