The recent development of new radionuclide detectors allows noninvasive outpatient monitoring of left ventricular function. This study was aimed at describing a new radionuclide technique useful to monitor cardiac function and at evaluating its potential clinical applications. We studied 14 normal subjects, 30 patients with coronary artery disease and 25 patients with dilated cardiomyopathy. Left ventricular function was continuously monitored in control conditions at rest, during daily physical activity of different intensity (walking on a level surface and climbing stairs), and during bicycle exercise. Left ventricular ejection fraction (EF) variability during recording in control conditions at rest was 0.2 +/- 1.8%. A significant relationship between outpatient EF at rest and conventional equilibrium radionuclide angiography was observed (r = 0.97, n = 69, p less than 0.001). In normal subjects both daily physical activity and exercise stress test induced an increase in heart rate and EF. In patients with coronary artery disease and in patients with dilated cardiomyopathy a heterogeneous EF response was observed during physical activity and exercise stress test. Our results demonstrate that this technique can be used for the ambulatory monitoring of left ventricular function in both normal subjects and patients with different types of cardiomyopathies.