Computed tomographic (CT) images of in vitro hearts filled with iodinated contrast medium have delineated right and left ventricular cavities, papillary muscles, major trabeculae, pulmonary artery, and the aorta. Because of relatively good structural definition, this study was undertaken to determine the potential use of CT in the measurement of cardiac dimensions and cavity volumes. Ten isolated arrested canine hearts were filled with an iodinated oil-paraffin mixture and scanned transversely from base to apex. Measurements of the thickness of the interventricular septum and of the left ventricular posterior wall (indexes of cardiac hypertrophy) had a high degree of correlation to similar measurements of corresponding heart specimens. Using serial tomographic images, the cavity volumes of individual tomographic scans were totaled. The volume of each scan of given thickness was obtained either by the use of planimetry or from a numerical computer printout. Both the planimetric and computer methods gave right and left ventricular volumes which correlated well (P less than .05) with the volumes of paraffin casts. Unlike other techniques widely used for ventricular volume measurement, the method described does not depend on an assumption that the chamber resembles a specific geometric model. This method of volume measurement is applicable to both the left ventricle, regardless of its shape, and to the concave irregularly shaped right ventricle.