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We have modified impedance cardiography for monitoring cardiac output during stress tests. Employing an off-line microcomputer, our instrument ensemble averaged impedance signals to minimize the effect of motion artifacts. We proposed a new four-spot electrode array and replaced the usual encircling band electrode array with it. We tested ten normal subjects and compared the signal-to-noise ratio (SNR) from our spot electrode array to that from a typical band electrode array at rest and during four levels of exercise on a treadmill. The average of the sighal-to-noise ratios for ten subjects from our spot electrode array was 13.6-45.5 percent larger than that from the band electrode array at rest and during four levels of exercise. Thus, it is desirable to replace band electrodes with spot electrodes in impedance cardiography for exercising subjects.