Assessment of ventricular function with an ambulatory left ventricular function monitor. Changes in ventricular function caused by activities of daily living, including standing, walking, stair climbing, and mental stress, were evaluated using a radionuclide device that recorded left ventricular function on a beat-by-beat basis. The ambulatory monitor was positioned over the patient's left ventricle after a gated blood pool scan. Monitoring revealed a 10% increase of left ventricular ejection fraction from baseline to brisk walking, an 18% increase during stair climbing, and a 6% increase with mental stress. In some subjects, however, the increase in ejection fraction during mental stress exceeded that during exercise. 