We describe a fully automated method for quantification of left ventricular performance by equilibrium radionuclide ventriculographic studies, based on subdivision of the left ventricular region into 9 equiangular sectors. The precise identification of the left ventricular contours is achieved by the use of morphological and functional criteria in a sequential edge detection algorithm with a success rate of 96%. In addition to left ventricular global and sectorial ejection fraction the first harmonic of the corresponding Fourier spectrum is approximated to each sectorial time-activity curve and to the global one. Sectorial phase is calculated as the difference between the phase of the sectorial and global first Fourier component. Computerized comparison between the sectorial parameters at rest and during peak exercise localizes and classifies the degree of global and regional impairment in response to exercise. The processing time of 60 sec makes this method suitable for routine use. The validity of our procedure has been tested in 34 patients before and after successful transluminal coronary angioplasty. In these patients, 73% of the stenosed vessels before dilatation were localized by sectorial ejection fraction, 77% by sectorial phases, and 88% by the combination of both.