The cardiac response to a variety of daily activities was assessed in 18 healthy adult subjects (mean age 31 years, range 21 to 39) with an ambulatory ventricular function monitor (VEST), which records serial beat-to-beat radionuclide and electrocardiographic data. The VEST was positioned and calibrated using data recorded during a multigated blood pool scan. It was worn for an average of 3.0 +/- 1.1 hours, while the subjects performed the following activities: sitting quietly (baseline); standing in place; walking; climbing stairs; bicycle or treadmill exercise; eating; sitting in a room at 4 degrees C for 20 minutes; and urinating. To calculate ejection fraction (EF), relative end-diastolic counts, relative cardiac output and heart rate, the beat-to-beat data were averaged over 15 to 30 seconds. Compared with baseline, standing increased EF by 0.03 +/- 0.04 and decreased end-diastolic volume by 10.9 +/- 4.7%. Walking and climbing stairs increased EF by 0.10 +/- 0.05 and 0.18 +/- 0.09, respectively, and increased end-diastolic volume by 7.8 +/- 5.3% and 12.8 +/- 4.3% (p less than 0.001). Eating increased EF by 0.02 +/- 0.03 and decreased end-diastolic volume by 11.3 +/- 6.1% (p less than 0.001). Cold stimuli and urinating decreased EF by 0.05 +/- 0.04 and 0.03 +/- 0.04, respectively (p less than 0.001 and less than 0.05). Serial left ventricular function monitoring during graded bicycle and treadmill exercise revealed a rapid increase in EF in the early stages of exercise, with no further change in the late stages. Heart rate and systolic blood pressure increased progressively with each successive stage.(ABSTRACT TRUNCATED AT 250 WORDS)