Objectives. We sought to assess the ability of preload-adjusted maximal power measured by echocardiographic automated border detection (ABD) to quantify left ventricular (LV) contractility by determining the effects of alterations in preload, afterload and contractile state. Background. Preload- adjusted maximal power can reflect LV contractile state relatively independent of changes in loading conditions. Methods. Eight anesthetized dogs had placement of aortic electromagnetic flow probes, LV and arterial pressure catheters and inferior vena caval (IVC) occluders; four had placement of thoracic aortic balloon occluders. Echocardiographic ABD measures of cross-sectional area were used as a surrogate for LV volume, and flow was estimated as the first derivative of area with respect to time. Power was calculated as the product of flow and pressure. Results. Preload independence during vena caval occlusions was achieved by preload adjustment (/ [end-diastolic area](3/2)). Afterload independence was demonstrated by preload-adjusted maximal power being unaffected by acute increases in LV systolic pressure induced by aortic occlusion. ABD preload-adjusted maximal power reflected changes in contractile state: increasing with dobutamine infusion from 36 ± 14 to 70 ± 15 mW/cm4 (p < 0.05 vs. control) and decreasing with propranolol infusion from 35 ± 13 to 17 ± 7 mW/cm4 (p < 0.05 vs. control). These changes were significantly correlated with calculations of preload-adjusted maximal power using aortic flow (r = 0.90, SEE 10.5 mW/cm4) and load-independent measures of end-systolic elastance from pressure-area loops (r = 0.90, SEE 10.6 mW/cm4). Calculations of normalized preload-adjusted maximal power using arterial pressure were also closely correlated with similar calculations using LV pressure (r = 0.99, SEE 3%). Conclusions. Preload-adjusted mammal power using echocardiographic ABD can predict LV contractile state relatively independent of loading conditions and has potential for clinical application.