To provide on-line quantification of left ventricular cavity dimensions and function by echocardiography 60 control subjects and 10 patients with cardiac dysfunction were studied. A novel, ultrasound imaging system was used which was developed to detect and track, in real time, ventricular endocardial blood boundaries based on quantitative assessment of acoustic properties of tissue. In addition, lateral gain compensation, a robust and novel image enhancement procedure, was used to provide instantaneous measurement and display of cavity areas and functional indexes on a beat-by-beat basis within regions of interest drawn around the blood pool cavity. In control subjects, shortaxis end-diastolic area averaged 13.1 ± 3.7 cm2 (SD), end-systolic area 5.9 ± 2.7 cm2, and fractional area change 55.6 ± 11.2%. Apical views yielded corresponding values of 23.8 ± 4.5 cm2, 15.5 ± 3.4 cm2 and 34.7 ± 7.8%. Instantaneous peak rate of cavity area change approximated 50 cm2/s in systole and 60 cm2/s in diastole in each view. Serial measurements of area and functional index were reproducible over intervals of 2 to 3 weeks. Patients with dilated ventricles exhibited average apical view area values of 49.1 ± 6.1 cm2 and 43.1 ± 4.9 cm2 in diastole and systole with a fractional area change of 12.2 ± 3.0%. Thus, results with on-line echocardiographic backscatter imaging-assisted automated edge detection are reproducible and capable of delineating cardiac dysfunction conveniently, promptly and serially at the bedside.