To develop an approach for on-line quantification of left ventricular size and function during pharmacological stress testing we employed echocardiographic automatic edge detection via integrated backscatter imaging during dobutamine infusion in 27 patients. Ventricular cavity areas, fractional area change and rate of cavity area change were obtained on-line with instantaneous graphic display of the data. When compared to baseline image data, patients with a normal response exhibited modest (15%) reduction in end-diastolic cavity areas at peak dobutamine level, but marked (33%) reduction in systolic areas yielding a 52% increase in fractional area change (n = 13; P < 0.001). The second group of patients (n = 14) had an abnormal response characterized by limited changes in measured parameters of ventricular function and reduced fractional area change (P < 0.05). On-line quantification during pharmacological stress echocardiography is a promising addition to the test for surveillance and objective instantaneous evaluation of global cardiac responses.