Computed tomography (CT) provides a noninvasive technique with high resolution cross-sectional tomographic images which allow volume measurements of an object, independent of its geometric configuration. A phantom of known volume with controllable periodic motion was used to validate the CT method of volume determination. A good correlation (P less than 0.05) was achieved. Missing angle reconstruction algorithms for gating were applied to estimate left ventricular volumes and ejection fraction in an experimental animal, and the results compared with a standard angiographic method. Left ventricular volumes correlated poorly, whereas the ejection fraction obtained correlated well (r = 0.9). The discrepancies may be attributed in part to the CT method in which difficulties were recognized in defining the left ventricular borders at the base of the heart and partial volume effect, and in part to inaccuracies in the standard angiographic method. Once validated, this method has been applied to the animal model in the form of a pilot study.