Pressure-volume relations are important means used to assess left ventricular (LV) contractility; however, on-line volume acquisition has been limited to the invasive conductance catheter. The objective was to compare simultaneous measures of LV volume by transesophageal echocardiographic automated border detection (ABD) and conductance catheter and their respective pressure-volume relations during steady state and alterations in preload and contractility. Seven dogs had placement of high-fidelity pressure and conductance catheters, a vena caval balloon occluder, and a transesophageal probe. An automated Simpson's rule volume algorithm was used from the transverse four-chamber view. Inotropic modulation was induced with dobutamine in four dogs and propranolol in three. Relative changes in ABD volume were linearly related to conductance volume at steady state with group mean r = 0.93 ± 0.03, standard error of estimate (SEE) = 10 ± 2%. Changes in end-diastolic volume, end-systolic volume, and stroke work with caval occlusion were also significantly correlated: r = 0.93 ± 0.04, SEE = 3.6 ml; r = 0.89 ± 0.04, SEE = 3.8 ± 1.9 ml; and r = 0.86 ± 0.05, SEE = 40 ± 21 mJ, respectively. The overall bias was for absolute ABD volume to be less. Endsystolic and maximal elastance values by ABD were significantly higher than by the conductance method; baseline group average 4.97 ± 0.92 mm Hg/ml versus 2.70 ± 1.15 mm Hg/ml and 6.63 ± 1.66 mm Hg/ml versus 3.20 ± 1.37 mm Hg/ml (p < 0.05), respectively. However, the direction and relative magnitude of changes in elastance with inotropic modulation were similar.