A recently developed contour tracking method provides automated edge detection of left ventricular endocardium without a region of interest. The accuracy of this automated contour tracking (ACT) method in the evaluation of left ventricular ejection fraction was assessed in 20 patients (16 males and 4 females, mean age 58 years) using both the ACT method and equilibrium radionuclide angiography. Ejection fractions measured by the ACT method correlated well with those measured by equilibrium radionuclide angiography (y = 0.8x + 11.9, r = 0.91, SEE = 4.0%, p < 0.01). The ACT method provides an accurate estimate of left ventricular ejection fraction.